Field of the invention

The present invention relates to an antimicrobial cleansing composition. It particularly relates to solid cleansing compositions containing oligodynamic metal based antimicrobial agent. Such cleansing compositions are particularly prone to discoloration owing to the inherent instability of the metal.

Background of the invention

Global demand for antimicrobial cleansing compositions is on the rise. Antimicrobial soap bars and compositions for cleaning hands and body are increasingly found to be preferred by consumers.

Antimicrobial cleansing compositions containing oligodynamic metals like silver, copper or zinc are very effective against a variety of bacteria. Silver is most widely used . However, some metals, especially silver, are particularly prone to destabilization when exposed to high pH, heat and strong sunlight which cause darkening or agglomeration or under extreme conditions, even phase separation.

Usually such metals are included at ppm or ppb (parts per million/parts per billion) levels which make it imperative to preserve their activity.

It is well-known that silver-based agents provide excellent antimicrobial properties, but aesthetic problems due to discoloration is a major concern. This is believed to be due to causes like inherent thermal and photo-instability of silver ions, along with other mechanisms. A wide range of silver salts is known to be thermally and photolytically unstable, discolouring to form brown, grey or black products. Silver ions may be formally reduced to its metallic state, assuming various physical forms and shapes (particles and filaments), often appearing brown, grey or black in colour. Reduced forms of silver that form particles of sizes of the order of the wavelength of visible light may also appear pink, orange, yellow or beige due to light scattering effects.

Silver based antimicrobial agents act quickly against some of the Gram Negative bacteria. However, such silver compounds generally tend to destabilize and darken over a period. In view of this phenomenon, the composition per se, especially soap bars, also tend to darken or discolor. This presents a technical problem which manifests itself after production and usually at the time of storage.

US 2003235623 A (TEVAN BV) discloses wide spectrum disinfecting and antiseptic composition for use in the fields of human medicine, veterinary science and industry, characterized because it includes: Hydrogen peroxide, lactic acid and halogen salts (Br, I) and/or salts of heavy metals (for example, silver halides) with surfactant agents, either cationic, like chlorhexidine and/or quaternary ammonium salts, like didecyl- methyl-polyoxy-ethyl-ammonium propionate, chlorides of ammonium or compounds of ammonium propylamide or anionic, like lauryl sulphate, dodecyl sulphate or alkyl succinic salts, with suitable excipients, some of which may be ethyl or isopropyl alcohol, chlorhexidine, non-chlorinated quaternary ammonium salts, like didecyl- methyl-polyoxy-ethyl-ammonium propionate, combined or not with iodine, and/or its salts, together with excipients, some of which may be ethyl or isopropyl alcohol. The document discloses the use of high levels of hydrogen peroxide and low levels of surfactant.

DE 102007003693 A (LANDMANN JOHANN) discloses silver and hydrogen peroxide containing disinfectants, characterized by the following composition per litre: 5 to 100 g solution mediator, 5 to 70 g hydrogen peroxide, 5 to 70 g surfactant, 0.1 to 20 mg colloidal silver, and water as the rest.

W0151 13785 A1 (UNILEVER) discloses a cleansing composition having pH of at least 9, said composition comprising: (i) 20 to 85 wt % anionic surfactant; and, (ii) a silver(l) compound having silver ion solubility (in water at 25 °C) of at least 1 x 10 ^"4 mol/L, at a level equivalent to silver content of 0.01 to 100 ppm, wherein the free alkali content of the composition is less than 0.01 percent. The composition is a robust and improved cleansing composition with a stable color.

W0151 13782 A1 (Unilever) discloses a cleansing composition comprising a surfactant, an oligodynamic metal or ions thereof, a chelating agent and a polymer having a group comprising a site having one or more lone pair of electrons wherein the surfactant is soap. The polymer having a group comprising a site having one or more lone pair of electrons enhances antimicrobial efficacy of the oligodynamic metal. W0151 13785 A1 (Unilever) discloses a cleansing composition having pH of at least 9. The compositions comprise 20 to 85 % by wt anionic surfactant and a silver (I) compound having silver ion solubility (in water at 25 °C) of at least 1 x 10 ^"4 moi/L at a level equivalent to silver content of 0,01 to 100 ppm. The free alkali content of said composition is less than 0,01 %, The composition is a robust improved cleansing composition with stable colour.

US2012003326 A (Henkel) discloses antibacterially active detergent, cleaning agent, after- treatment agent or washing aid that contains elementary silver and/or a silver compound as an antibacterial component, an aldehyde component, and hydrogen peroxide to stabilize the aldehydes against oxidation by silver. US2012003289 A (Henkel) discloses an auxiliary washing aid comprising a textile substrate coated or otherwise impregnated with a composition comprising elementary silver and/or a silver compound, non-neutralized fatty acid, and hydrogen peroxide.

US1993686A (Degussa, 1935) discloses silver-containing soaps which disinfect and do not discolour. They are obtained by mixing with soap metallic silver in the form of powder, foil, leaves, flakes, or the like. The silver is activated by superficial electrolytic oxidation or by treatment with hydrogen peroxide, permanganate, or other oxidizing agent. There may also be added soluble or difficultly soluble silver compounds, or/and sodium perborate, sodium pyrophosphate peroxide, or other substance containing active oxygen.

There still remains an unmet need for faster acting and efficacious antimicrobial compositions.

There is also a need to provide an efficacious antimicrobial cleansing composition which allows incorporation of higher levels of oligodynamic metal without discoloration.

Summary of the invention

According to the first aspect of the present invention, there is provided a method of improving personal hygiene, comprising a step of applying to the body a cleansing composition comprising surfactant from 20% to 85% by weight of the composition; oligodynamic metal from 0.00001 % to 0.01 % by weight of the composition; and peroxide from 0.001 % to 2% by weight of the composition. According to another aspect of the invention there is provided a method of inhibiting microbial growth on a surface comprising the steps of: applying a composition of the first aspect of the invention to the surface; and rinsing the surface with a suitable solvent. According to yet another aspect of the present invention is provided use of a composition comprising the composition of first aspect of the invention for improving personal hygiene.

These and other aspects, features and advantages will become apparent to those of ordinary skill in the art from a reading of the following detailed description and the appended claims. For the avoidance of doubt, any feature of one aspect of the present invention may be utilized in any other aspect of the invention. The word "comprising" is intended to mean "including" but not necessarily "consisting of" or "composed of." In other words, the listed steps or options need not be exhaustive. It is noted that the examples given in the description below are intended to clarify the invention and are not intended to limit the invention to those examples per se. Similarly, all percentages are weight/weight percentages unless otherwise indicated.

Detailed description of the invention

Except in the operating and comparative examples, or where otherwise explicitly indicated, all numbers in this description indicating amounts of material or conditions of reaction, physical properties of materials and/or use are to be understood as modified by the word "about". Unless specified otherwise, numerical ranges expressed in the format "from x to y" are understood to include x and y. When for a specific feature multiple preferred ranges are described in the format "from x to y", it is understood that all ranges combining the different endpoints are also contemplated. The cleansing composition used in the method of the present invention comprises surfactant, oligodynamic metal and peroxide. Various components of the antimicrobial composition are described below. The compositions of the present invention are preferred for non-therapeutic use, and more particularly preferred for use in cleaning surfaces of human body including skin, hair or oral cavity or for hard surface cleaning applications in a cosmetic manner. Oligodynamic metal based antimicrobial agents have very good antimicrobial effect. However such metals often tend to discolor under alkaline conditions. It often leads to discoloration of the product itself, particularly in the case of soap bars. This effect, though undesirable, is more prominent in the case of bars which are lighter in color and more so with white soap bars. Discoloration tends to intensify over a period and with increase in temperature, and often it is found that the change is irreversible.

The discoloration is believed to be caused by susceptibility of oligodynamic metal ions to heat and light. A wide range of oligodynamic metal salts is thermally and photo- chemically unstable, discoloring to form brown, gray or black particles. As described earlier, discoloration is too prominent to be ignored and is believed to be accelerated by alkalinity in view of increased solubility of oligodynamic metal salts. The challenge for oligodynamic metal incorporation in soap leading to discoloration of the soap bars was found to due to high alkalinity of the formulation.

Present inventors have surprisingly found that compositions comprising selected ingredients, namely oligodynamic metal, a peroxide and surfactant, in selective amounts result in antimicrobial compositions with high color stability even when pH of the composition is very high.

The present invention provides a method of improving personal hygiene, comprising a step of applying to the body a cleansing composition comprising surfactant from 25 to 85 wt%, oligodynamic metal ranging from 0.00001 wt% to 0.01 wt% and peroxide ranging from 0.001 wt% to 2 wt% based on the weight of the composition.

The present inventors surprisingly found that by adding peroxides at a particular concentration helped to formulate oligodynamic metal at higher levels without discoloration issues. Various components of the composition are described in detail below.

The cleansing composition

The cleansing composition is preferably a solid composition and more preferably in the form of a bar. Surfactant

The cleansing composition contains a base of one or more surfactants to provide the basic cleansing action. The surfactant may be of any class such as anionic, cationic, non-ionic, amphoteric, zwitterionic or a mixture thereof and it can be chosen according to the end use.

Anionic surfactants are the most preferred as they provide good cleansing action and they are often used in variety of cleansing compositions.

The anionic surfactants may be soap-based ones which are sodium/potassium salts of long chain fatty acids. The cleansing compositions comprise 25 to 85 wt% surfactant, more preferably 25 to 75 wt%, still more preferably 30 to 70 wt% based on the weight of the composition. The type and total surfactant content will depend on the intended purpose of the

composition, for example, where the composition is bar of soap then it will

predominately contain fatty acid soaps. Where is a mild cleansing bar, it will predominately contain fatty acyl isethionate surfactant.

Usually the composition will contain a mixture of different types of surfactants.

Anionic surfactants are particularly preferred for the compositions of present invention. The anionic surfactant may be, for example, an aliphatic sulfonate, such as a primary alkane (e.g. C8 toC22) sulfonate, primary alkane (e.g., C8 to C22) disulfonate, C8 to C22 alkene sulfonate, C8to C22 hydroxyalkane sulfonate or alkyl glyceryl ether sulfonate (AGS); or an aromatic sulfonate such as alkyl benzene sulfonate. Alpha olefin sulfonates are also suitable as anionic surfactants. The anionic may also be an alkyl sulfate (e.g., C12 to C18 alkyl sulfate), especially a primary alcohol sulfate or an alkyl ether sulfate (including alkyl glyceryl ether sulfates). The anionic surfactant can also be a sulfonated fatty acid such as alpha sulfonated tallow fatty acid, a sulfonated fatty acid ester such as alpha sulfonated methyl tallowate or mixtures thereof. The anionic surfactant may also be alkyl sulfosuccinates (including mono- and dialkyl, e.g., C6 to C22 sulfosuccinates); alkyl and acyl taurates, alkyl and acyl sarcosinates,

sulfoacetates, C8 to C22 alkyl phosphates and phosphates, alkyl phosphate esters and alkoxyl alkyl phosphate esters, acyl lactates or lactylates, C8 to C2, monoalkyl succinates and maleates, sulphoacetates, and acyl isethionates. Another class of anionic surfactants is C8 to C20 alkyl ethoxy (1 to 20 EO) carboxylates. Yet another suitable class of anionic surfactant is C8 to C18 acyl isethionates. These esters are prepared by reacting alkali metal isethionates with mixed aliphatic fatty acids having from 6 to 18 carbon atoms and an iodine value of less than 20. At least 75% of the mixed fatty acids have from 12 to 18 carbon atoms and up to 25% have from 6 to 10 carbon atoms. The acyl isethionate may also be alkoxylated isethionates. The alkyl ether sulphates, alkyl ether sulphosuccinates, alkyl ether phosphates and alkyl ether carboxylic acids and salts thereof may contain from 1 to 20 ethylene oxide or propylene oxide units per molecule.

Typical anionic cleansing surfactants for use in the compositions include sodium oleyl succinate, ammonium lauryl sulphosuccinate, sodium lauryl sulphate, sodium lauryl ether sulphate, sodium lauryl ether sulphosuccinate, ammonium lauryl sulphate, ammonium lauryl ether sulphate, sodium dodecylbenzene sulphonate, triethanolamine dodecylbenzene sulphonate, sodium cocoyl isethionate, sodium lauryl isethionate, lauryl ether carboxylic acid and sodium N-lauryl sarcosinate.

In a preferred aspect of the present invention, the surfactant selected from the group comprising an anionic surfactants. These includealkyi sulphates, fatty acid amides and linear alkyl benzene sulphonates or combinations thereof. It is further preferable that the surfactant comprises soap.

A particularly preferred format for compositions is a soap bar which can be used for bodywash as well as hand wash. This format contain a major proportion of fatty acid soap as the anionic surfactant.

The term "fatty acid soap" or, more simply, "soap" is used here in its popular sense. Reference to fatty acid soaps is to the fatty acid in neutralized form. Preferably the fatty acid from which the soap is derived is substantially completely neutralized in forming the fatty acid soap, that is say at least 95%, more particularly at least 98%, of the fatty acid groups thereof have been neutralized. The term "soap" is used herein to mean an alkali metal or alkanol ammonium salts of aliphatic, alkane-, or alkene monocarboxylic acids usually derived from natural triglycerides. Sodium, potassium, magnesium, mono-, di- and tri-ethanol ammonium cations, or combinations thereof, are the most suitable.

Preferably a blend of fatty acids is used from which blend of fatty acid soaps is prepared. The term "soap" refers to Sodium, Potassium, Magnesium, mono-, di- and tri-ethanol ammonium cation or combinations thereof. In general, Sodium soaps are used in the compositions of this invention, but up to 15% of the soap content may be some other soap forms such as Potassium, Magnesium or triethanolamine soaps.

Soaps having the fatty acid distribution of coconut oil and palm kernel oil may provide the lower end of the broad molecular weight range. Those soaps having the fatty acid distribution of peanut or rapeseed oil, or their hydrogenated derivatives, may provide the upper end of the broad molecular weight range. It is preferred to use soaps having the fatty acid distribution of coconut oil or tallow, or mixtures thereof, since these are among the more readily available triglyceride fats. The proportion of fatty acids having at least 12 carbon atoms in coconut oil soap is about 85%. This proportion will be greater when mixtures of coconut oil and fats such as tallow, palm oil, or non-tropical nut oils or fats are used, wherein the principle chain lengths are C16 and higher.

Preferred soap for use in the compositions has at least about 85% fatty acids having about 12 to 18 carbon atoms. The preferred soaps for use in the present invention should include at least about 30% saturated soaps, i.e., soaps derived from saturated fatty acids, preferably at least about 40%, more preferably about 50%, saturated soaps by weight of the fatty acid soap. Soaps can be classified into three broad categories which differ in the chain length of the hydrocarbon chain, i.e., the chainlength of the fatty acid, and whether the fatty acid is saturated or unsaturated. For purposes of the present invention these classifications are: "Laurics" soaps which encompass soaps which are derived predominantly from C12 to C14 saturated fatty acid, i.e. lauric and myristic acid, but can contain minor amounts of soaps derived from shorter chain fatty acids, e.g., C10. Laurics soaps are generally derived in practice from the hydrolysis of nut oils such as coconut oil and palm kernel oil.

"Stearics" soaps which encompass soaps which are derived predominantly from C16 to C18 saturated fatty acid, i.e. palmitic and stearic acid but can contain minor level of saturated soaps derived from longer chain fatty acids, e.g., C20. Stearics soaps are generally derived in practice from triglyceride oils such as tallow, palm oil and palm stearin.

Oleics" soaps which encompass soaps which are derived from unsaturated fatty acids including predominantly oleic acid (C18:1 ), linoeleic acid( (C18:2), myristoleic acid (C14:1 ) and palmitoleic acid (C16:1 ) as well as minor amounts of longer and shorter chain unsaturated and polyunsaturated fatty acids. Oleics soaps are generally derived in practice from the hydrolysis of various triglyceride oils and fats such as tallow, palm oil, sunflower seed oil and soybean oil. Coconut oil employed for the soap may be substituted in whole or in part by other "high-laurics" or "laurics rich" oils, that is, oils or fats wherein at least 45% of the total fatty acids are composed of lauric acid, myristic acid and mixtures thereof. These oils are exemplified by tropical nut oils of the coconut oil class. For instance, they include: palm kernel oil, babassu oil, ouricuri oil, tucum oil, cohune nut oil, murumuru oil, jaboty kernel oil, khakan kernel oil, dika nut oil, and ucuhuba butter. It is preferable to keep the level of unsaturated soap to a minimum.

Soap may be made by the classic kettle boiling process or modern continuous soap manufacturing processes wherein natural fats and oils such as tallow, palm oil or coconut oil or their equivalents are saponified with an alkali metal hydroxide using procedures well known to those skilled in the art. Two broad processes are of particular commercial importance. The SAGE process where triglycerides are saponified with a base, e.g., sodium hydroxide, and the reaction products extensively treated and the glycerin component extracted and recovered. The second process is the SWING process, where the saponification product is directly used with less exhaustive treatment and the glycerin from the triglyceride is not separated but rather included in the finished soap noodles and/or bars. Alternatively, the soaps may be made by neutralizing fatty acids (e.g., distilled fatty acids), such as lauric (C12), myristic (C14), palmitic (C16), stearic (C18) and oleic acid (C18:1 ) acids and their mixtures with an alkali metal hydroxide or carbonate.

Where amphoteric surfactants are used, it is preferred that such surfactants include at least one acid group. This may be a carboxylic or a sulphonic acid group. They include quaternary nitrogen and therefore are quaternary amido acids. They should generally include an alkyi or alkenyl group of 7 to 18 carbon atoms. Suitable amphoteric surfactants include amphoacetates, alkyi and alkyi amido betaines, and alkyi and alkyi amido sulphobetaines. Amphoacetates and diamphoacetates are also intended to be covered in possible zwitterionic and/or amphoteric compounds which may be used. Zwitterionic surfactants may also be present in some compositions of this invention. Zwitterionic surfactants suitable for use herein include, but are not limited to derivatives of aliphatic quaternary ammonium, phosphonium, and sulfonium compounds, in which the aliphatic radicals can be straight or branched chain, and wherein one of the aliphatic substituents contains from about 8 to about 18 carbon atoms and one substituent contains an anionic group, e.g., carboxy, sulfonate, sulfate, phosphate, or phosphonate. Illustrative zwitterionics are coco dimethyl carboxymethyl betaine, cocoamidopropyl betaine, cocobetaine, oleyl betaine, cetyl dimethyl carboxymethyl betaine, lauryl bis-(2-hydroxyethyl) carboxymethyl betaine, stearyl bis-(2- hydroxypropyl) carboxymethyl betaine, oleyl dimethyl gamma-carboxypropyl betaine, lauryl bis-(2-hydroxpropyl)alpha-carboxyethyl betaine, and mixtures thereof. The sulfobetaines may include stearyl dimethyl sulfopropyl betaine, lauryl dimethyl sulfoethyl betaine, lauryl bis-(2-hydroxyethyl) sulfopropyl betaine and mixtures thereof.

The amount of zwitterionic surfactant depends on the amount of other surfactants and also the nature and format of the cleansing compositions. Suitable nonionic surfactants include the reaction products of compounds having a hydrophobic group and a reactive hydrogen atom, for example aliphatic alcohols or fatty acids, with alkylene oxides, especially ethylene oxide either alone or with propylene oxide. Examples include the condensation products of aliphatic (C8-C18) primary or secondary linear or branched alcohols with ethylene oxide, and products made by condensation of ethylene oxide with the reaction products of propylene oxide and ethylenediamine. Other so-called nonionic detergent compounds include long chain tertiary amine oxides, long chain tertiary phosphine oxides and dialkyl sulphoxides. The nonionic may also be a sugar amide, such as alkyi polysaccharides and alkyi polysaccharide amides. Examples of some cationic surfactants which may be used are the quaternary ammonium compounds such as alkyldimethylammonium halides. Detailed account of other surfactants can be found in "Surface Active Agents and Detergents" (Vol. I & II) by Schwartz, Perry & Berch.

Peroxide Compounds

Peroxide compounds are a class of chemical compounds in which two oxygen atoms are linked together by a single covalent bond. Several organic and inorganic peroxides are useful as bleaching agents, as initiators of polymerization reactions, and in the preparation of hydrogen peroxide and other oxygen compounds. The negatively charged peroxide ion (O2 ^2" ) is present in inorganic compounds that may be regarded as salts of the very weak acid hydrogen peroxide; examples are sodium peroxide (Na2C>2), a bleaching agent, and barium peroxide (BaC>2), formerly used as a source of hydrogen peroxide.

Two categories of peroxides exist in which one or both of the oxygen atoms are covalently linked to atoms other than hydrogen. One category is represented by cumene hydroperoxide, an organic compound used as a polymerization initiator and as a source of phenol and acetone, and peroxysulfuric acid, an inorganic compound used as an oxidizing agent. The other category includes di-fe/t-butyl peroxide and ammonium peroxydisulfate, both used as initiators.

The peroxides in the composition range from 0.001 % to 2% by weight of the composition, more preferably from 0.01 to 1 wt% and more preferably from 0.03 to 0.5 wt%.

The peroxides for use in the present invention preferably include but are not limited to hydroperoxide, superoxides, dioxygenyls, ozones, ozonides or mixtures thereof, more preferably the peroxides comprise hydroperoxides and most preferably hydrogen peroxide. Inorganic peroxides can be ionic and covalent peroxide. The first class mostly contains the peroxides of the alkali and alkaline earth metals whereas the covalent peroxides are represented by hydrogen peroxide and peroxymonosulfuric acid (H2SO5). In contrast to the purely ionic character of alkali metal peroxides, peroxides of transition metals have a more covalent character. It should be noted that in some older literature some high-valence metal oxides are incorrectly named peroxides (e.g. PbC>2, MnC>2, Ag404) even though they do not contain the peroxide ion.

Organic peroxides can be divided into two major classes, peroxy acids and organic hydroperoxides

Hydroperoxides are a particularly preferred class of peroxides for the present invention. Hydroperoxides contain the 0-O-H ^" unit. Hydrogen peroxide is therefore also an example of a hydroperoxide. One of the most commonly used hydroperoxides is called i-butyl hydroperoxide (or fe/t-butyl hydroperoxide).

In a highly preferred aspect of the present invention the peroxide is a hydrogen peroxide, shown below with a peroxo unit.

hydrogen pe roxfcfc

The peroxide value (PV) is a figure used for determining the peroxide oxygen

(especially hydroperoxides). It is expressed in milliequivalents of active oxygen per 1 kg of fat.

The Oligodynamic metal

The cleansing composition contains a metal having oligodynamic activity. It (also called as oligodynamic action) is the effect of inhibiting, or killing micro-organisms by the use of very small amounts of a chemical substance. Several metals exhibit such an effect. Preferred metals are silver, copper, zinc or gold. Silver is particularly preferred. In the ionic form it may exist as a salt or any compound in any applicable oxidation state.

The cleansing composition of the present invention comprises 0.00001 to 0.01 wt% of oligodynamic metal. It is preferred that the metal is present in the form of a compound and more preferably a compound of silver; then an appropriate amount of the compound is included so that the active metal content is within the broad and preferred ranges as already indicated. The compound is present more preferably from 0.0001 wt% to 0.005 wt% and most preferably from 0.0003 to 0.0015 wt%.

It is preferred that the %weight ratio of peroxide to oligodynamic metal is in the range of 0.5:1 to 2000:1 , more preferably in the range of 10:1 to 500:1 and most preferably in the range of 25:1 to 100:1 .

Silver (I) Compound

It is preferred that the cleansing composition of the present invention contains silver as the oligodynamic metal. It is further preferred that Silver is included in the form of Silver(l) compound but may also be in the form of particles, eg., nanoparticles. Silver(l) compounds are one or more water-soluble silver(l) compounds having silver ion solubility at least 1 .0 x10 ^"4 mol/L (in water at 25°C). Silver ion solubility, as referred to herein, is a value derived from a solubility product (Ksp) in water at 25°C, a well known parameter that is reported in numerous sources. More particularly, silver ion solubility [Ag+], a value given in mol/L may be calculated using the formula: [Ag+] = (Ksp · x)< ^1/ <x ⁺¹ » , wherein Ksp is the solubility product of the compound of interest in water at 25°C, and x represents the number of moles of silver ion per mole of compound. It has been found that Silver (I) compounds having a silver ion solubility of at least 1 x 10 ^"4 mol/L in are suitable for use herein. Silver ion solubility values for a variety of silver compounds are given in Table 1 :

TABLE 1

Ksp

(mol/L in water Silver Ion Solubility [Ag+]

Silver Compound X at 25 °C) (mol/L in water at 25 °C).

silver nitrate 1 51 .6 7.2

Silver acetate 1 2.0 x 10 ^"3 4.5 x 10 ^"2

Silver sulfate 2 1.4 x 10 ^"5 3.0 x 10 ^"2

Silver benzoate 1 2.5 x 10 ^"5 5.0 x 10 ^"3

Silver salicylate 1 1.5 x 10 ^"5 3.9 x 10- ³

Silver carbonate 2 8.5 x 10 ^"12 2.6 x 10 ^"4 Silver citrate 3 2.5 x 10- ¹⁶ 1 .7 x 10- ⁴

Silver oxide 1 2.1 x 10- ⁸ 1 .4 x 10- ⁴

Silver phosphate 3 8.9 x 10 ^"17 1 .3x 10- ⁴

Silver chloride 1 1.8 x 10- ¹⁰ 1 .3 x 10- ⁵

Silver bromide 1 5.3 x 10- ¹³ 7.3 x 10- ⁷

Silver iodide 1 8.3 x 10- ¹⁷ 9.1 x 10- ⁹

Silver sulfide 2 8.0 x 10- ⁵¹ 2.5 x 10 ^"17

In preferred compositions, silver is present in the form of a compound selected from silver oxide, silver nitrate, silver acetate, silver sulfate, silver benzoate, silver salicylate, silver carbonate, silver citrate or silver phosphate. In particularly preferred compositions the silver(l) compound is silver oxide. The compounds are added in amounts equivalent to the silver content. This can be easily determined by knowing the molecular formula and the relative molecular mass of the concerned silver-based compound.

Optional and preferred ingredients In addition to the ingredients described earlier, preferred embodiments of the cleansing compositions may also include other optional and preferred ingredients for their known benefits. The type and content will largely depend on the nature and type of cleansing composition as well as general principles of formulation science.

It is preferred that the composition contains free fatty acids. Preferred embodiments contain 0.01 wt% to 10 wt% free fatty acid, especially when major portion of the surfactant is soap based. Potentially suitable fatty acids are C8 to C22 fatty acids. Preferred fatty acids are C12 to C18, preferably predominantly saturated, straight-chain fatty acids. However, some unsaturated fatty acids can also be employed. Of course the free fatty acids can be mixtures of shorter chain length (e.g., C10 to C14) and longer chain length (e.g., C16 to C18) chain fatty acids. For example, one useful fatty acid is fatty acid derived from high-laurics triglycerides such as coconut oil, palm kernel oil, and babasu oil. The fatty acid can be incorporated directly or they can be generated in-situ by the addition of a protic acid to the soap during processing. Examples of suitable protic acids include: mineral acids such as hydrochloric acid and sulfuric acid, adipic acid, citric acid, glycolic acid, acetic acid, formic acid, fumaric acid, lactic acid, malic acid, maleic acid, succinic acid, tartaric acid and polyacrylic acid. However, care should be taken that the residual electrolyte in the bar does not substantially reduce the effectiveness of the anti-cracking agent. The level of fatty acid having a chain length of 14 carbon atoms and below should generally not exceed 5.0%, preferably not exceed about 1 % and most preferably be 0.8% or less based on the total weight of the continuous phase.

Other optional compositions include one or more skin benefit agents. The term "skin benefit agent" is defined as a substance which softens or improves the elasticity, appearance, and youthfulness of the skin (stratum corneum) by either increasing its water content, adding, or replacing lipids and other skin nutrients; or both, and keeps it soft by retarding the decrease of its water content. Included among the suitable skin benefit agents are emollients, including, for example, hydrophobic emollients, hydrophilic emollients, or blends thereof. Water-soluble skin benefit agents may optionally be formulated into the liquid compositions of the invention. A variety of water- soluble skin benefit agents can be used and the level can be from 0 to 50% but preferably from 1 to 30% by weight of the composition. These materials include, but are not limited to, polyhydroxy alcohols. Preferred water soluble skin benefit agents are glycerin, sorbitol and polyethylene glycol.

Water-insoluble skin benefit agents may also be formulated into the compositions as conditioners and moisturizers. Examples include silicone oils; hydrocarbons such as liquid paraffins, petrolatum, microcrystalline wax, and mineral oil; and vegetable triglycerides such as sunflower seed and cottonseed oils.

Water soluble/dispersible polymers is an optional ingredient that is highly preferred to be included in composition. These polymers can be cationic, anionic, amphoteric or nonionic types with molecular weights higher than 100,000 Dalton. They are known to increase the viscosity and stability of liquid cleanser compositions, to enhance in-use and after-use skin sensory feels, and to enhance lather creaminess and lather stability. Amount of the polymers, when present, may range from 0.1 to 10% by weight of the composition. Preservatives can also be added into the compositions to protect against the growth of potentially harmful microorganisms. Suitable traditional preservatives for compositions of this invention are alkyl esters of para-hydroxybenzoic acid. Other preservatives which have, more recently come into use, include hydantoin derivatives, propionate salts, and a variety of quaternary ammonium compounds. Particularly preferred preservatives are phenoxyethanol, methyl paraben, propyl paraben, imidazolidinyl urea, sodium dehydroacetate and benzyl alcohol. The preservatives should be selected having regard for the use of the composition and possible incompatibility between the preservatives and other ingredients. Preservatives are preferably employed in amounts ranging from 0.01 % to 2% by weight of the composition.

A variety of other optional materials may be formulated into the compositions. These may include: antimicrobials such as 2-hydroxy-4,2',4'-trichlorodiphenylether (triclosan), 2,6-dimethyl-4-hydroxychlorobenzene, and 3,4,4'-trichlorocarbanilide; scrub and exfoliating particles such as polyethylene and silica or alumina; cooling agents such as menthol; skin calming agents such as aloe vera; and colorants.

In addition, the compositions may further include 0 to 10% by weight of opacifiers and pearlizers such as ethylene glycol distearate, titanium dioxide or Lytron® 621

(Styrene/Acrylate copolymer); all of which are useful in enhancing the appearance or properties of the product.

Soap bars in particular may contain particles that are greater than 50 μηη in average diameter that help remove dry skin. Not being bound by theory, the degree of exfoliation depends on the size and morphology of the particles. Large and rough particles are usually very harsh and irritating. Very small particles may not serve as effective exfoliants. Such exfoliants used in the art include natural minerals such as silica, talc, calcite, pumice, tricalcium phosphate; seeds such as rice, apricot seeds, etc; crushed shells such as almond and walnut shells; oatmeal; polymers such as polyethylene and polypropylene beads, flower petals and leaves; microcrystalline wax beads; jojoba ester beads, and the like. These exfoliants come in a variety of particle sizes and morphology ranging from micron sized to a few mm. They also have a range of hardness. Some examples are talc, calcite, pumice, walnut shells, dolomite and polyethylene. Also useful are sunscreen actives. Non limiting examples of sunscreens which are useful in the compositions of the present invention are those selected from the group consisting of octyl methoxyl cinnamate (Parsol® MCX) and butyl methoxy

benzoylmethane (Parsol® 1789), 2-ethylhexyl p-methoxycinnamate, 2-ethylhexyl N,N- dimethyl-p-aminobenzoate, p-aminobenzoic acid, 2-phenylbenzimidazole-5sulfonic acid, oxybenzone, mixtures thereof, and the like. Protease inhibitors are also useful. Protease inhibitors can be divided into two general classes: the proteinases and the peptidases. Proteinases act on specific interior peptide bonds of proteins and peptidases act on peptide bonds adjacent to a free amino or carboxyl group on the end of a protein and thus cleave the protein from the outside. The protease inhibitors suitable for use in the inventive personal toilet bar compositions include, but are not limited to, proteinases such as serine proteases, metalloproteases, cysteine proteases, and aspartyl protease, and peptidases, such as carboxypepidases, dipeptidases and aminopepidases, mixtures thereof and the like.

Other useful active ingredients are skin tightening agents. Non-limiting examples of skin tightening agents which are useful in the compositions of the present invention include monomers which can bind a polymer to the skin such as (meth)acrylic acid and a hydrophobic monomer comprised of long chain alkyl (meth)acrylates, mixtures thereof, and the like.

Active ingredients in the inventive personal toilet bar compositions may also include anti-itch ingredients. Suitable examples of anti-itch ingredients, which are useful in the compositions of the present invention, include hydrocortisone, methdilizine and trimeprazine, mixtures thereof, and the like. βΗ

It is preferred that the pH of the compositions ranges from 9 to 1 1. Antimicrobial effect The cleansing compositions disclosed herein have biocidal activity against Gram Positive bacteria, including, in particular, S. aureus. Other Gram Positive bacteria against which the compositions are of interest are S. epidermidis, and/or

Corynebacteria, in particular, Corynebacteria strains responsible for the hydrolysis of axilla secretions to malodorous compounds. Desirably, the bar provides a log-io reduction in biocial activity against Staphylococcus aureus ATCC 6538 of at least 2, preferably at least 3 more preferably at least 3.5 at a contact time of 30 seconds, and even more preferably provides a logio reduction against S aureus ATCC 6538 of at least 1 , preferably at least 1 .5 more preferably at least 2 at a contact time of 10 seconds.

The bar composition is diluted with water to form 1 to 25 wt% solution thereof, the resulting soap solution applied to the skin for contact times under 1 minute, typically 30 seconds or less with contact times of 10 to 30 seconds being of interest with respect to contact times of a moderate to relatively long duration and contact times of 10 seconds or less being of interest with respect to contact times of short to moderate duration, and thereafter is removed from the skin, typically by rinsing with water. Preferably the bars have a lather volume of at least 200 ml following the procedure of Indian Standard 13498:1997, Annex C.

Discoloration There is neither any standard definition nor a unified scale for discoloration, therefore it is often measured by ad hoc in-house methods. Usually some samples of the composition are picked at random and stored under different physical conditions of temperature.

In accordance with a typical protocol, samples were stored at 27°C, 37°C, 45°C and monitored over a period of a period of 12 weeks and at 50°C for a period of 4 weeks. The samples are intermittently observed by trained analysts for any visible signs of change in colour or in the general appearance. Usually the test lasts for a total period of twelve weeks. Samples are then graded and rated on a scale on the basis of appearance. The present invention provides a method of inhibiting microbial growth on a surface comprising the steps of applying a composition of the present invention on to the surface; and rinsing the surface with a suitable solvent.

The present invention provides use of a composition comprising 25% to 85% by weight surfactant, 0.00001 % to 0.01 % by weight oligodynamic metal, 0.001 % to 2% by weight of peroxide for improved personal hygiene. Examples

The invention will be demonstrated with examples. The examples are for purpose of illustration only and do not limit the scope of claims in any manner.

Example 1

The preferred Soap bars (PSB) were prepared according to formulation as indicated Table 2 (extruded bars) and Table 3 (cast melt bars).

TABLE 2

TABLE 3

Example 2: Color Stability

White colored compositions according to Tables 2 and 3 were made for this experiment.

The samples were stored at 27 °C, 37 °C, 45 °C and 50 °C and monitored over a period of a period of 12 weeks. Their color was particularly observed at fixed intervals throughout the period. Bars were said to have failed the test when they were discolored beyond acceptable level. The details of the scores are provided in Table 4.

The data in the table 5 indicate that each comparative composition failed the test while each experimental (preferred) soap compositions retained the initial color to an appreciable extent.

TABLE 4 : Details about the scores

A rating up to 3 was found to be ok for clearing the storage stability. Samples with ratings 4 and 5 are supposedly failed samples which could not clear storage stability test.

TABLE 5

Example 3: Antimicrobial Efficacy

Soap solution preparation The solid soap bar being evaluated is mixed with water and dissolved at 50 °C to give a 10 wt% solution. After dissolution, the resulting soap bar solution is equilibrated at 46 °C prior to performing the bactericidal assay procedure.

Bacteria Staphylococcus aureus ATCC 6538, were used in this study to represent Gram positive bacteria. The bacteria was stored at - 80 °C. Fresh isolates were cultured twice on Tryptic Soy Agar plates for 24 hours at 37 °C before each experiment.

In-Vitro Time-Kill Assay

Time-kill assays are performed according to the European Standard, EN 1040:2005 entitled "Chemical Disinfectants and Antiseptics - Quantitative Suspension Test for the Evaluation of Basic Bactericidal Activity of Chemical Disinfectants and Antiseptics - Test Method and Requirements (Phase 1 )". Following this procedure Growth-phase bacterial cultures at 1.5X10 ⁸ to 5 X10 ⁸ colony forming units per ml (cfu/ml) were treated with the 10wt.% soap bar solutions (prepared as described above) at 46°C. In forming the test samples, 8 parts by weight of the 10wt.% soap bar solution is combined with 1 part by weight of the culture and 1 part by weight of water, i.e., the concentration of the soap bar composition in the test samples is 8 wt.%. After 10, 30, and 60 seconds of exposure, samples were neutralized to arrest the antibacterial activity of the soap solutions. The resulting solutions were serially diluted, plated on solid medium, incubated for 24 hours and surviving cells were enumerated. Bactericidal activity is defined as the log reduction in cfu/ml relative to the bacterial concentration at 0 seconds. Cultures not exposed to any soap or silver solutions serve as no-treatment controls.

The log-io reduction was calculated using the formula: Logio Reduction = logio (numbers control) - logio (test sample survivors)

The antimicrobial (biocidal) activity of the bars so produced was evaluated following the protocol described earlier. Also evaluated were aqueous solutions of silver compound, formulated to a pH comparable to that of the soap solution (i.e., pH 10.7). Biocidal activity results are reported in Table 6. TABLE 6

The data as presented in Table 6 show that for an amount of 5 ppm (0.0005 wt%) of silver in a cast melt soap formulation, addition of hydrogen peroxide does not affect the antimicrobial efficacy of the composition. This data shows the method of improving personal hygiene in accordance with the invention.