Usually, cleansing/soap formulations are provided for the cleansing of skin with surface active preparations. Skin being a sensitive substrate, there is always the need to provide a formulation which would favour effective cleansing of the skin gently and without causing irritation or problems to the skin surface, and deliver benefit agents such as skin lightening, antibacterial agents, etc.

Based on the above requirements, various formulations of cleansing composition are made available to suit various end user benefits/utilities. Mildness is considered one of the key requirements to maintain proper skin benefits in the use of cleansing compositions. However, mildness is sometimes achieved at the expense of lathering and cleansing benefits.

In the alternative, in case of requirements of improved lathering characteristics, the same is often achieved by sacrificing mildness of the formulation. Therefore, depending upon the specific use and application, cleansing

formulations are tailor made. It is however difficult, and not always predictable as to the end properties and characteristics obtained of selective blends of fatty acid soaps and synthetic surfactants used.

US 5,607, 909 discloses a mild, lathering personal cleansing freezer bar composition by weight of the bar comprising from 30 to 85 parts of tailored fatty acid soap, from 3 parts to 30 parts synthetic surfactant and from 15 to 35 parts of water, wherein the tailored fatty acid soap is a mixture of 65% to about 95% sodium soap and 5 to about 35% magnesium soap (which is 1.5 % to 30 % magnesium soap in overall formulation). This prior art is specifically directed to a mild lathering bar, and essentially involves synthetic surfactants.

US 5,387, 362 relates to personal cleansing bar made with a base soap tailored with mixed counterions (Mg/K/Na), selected saturated C14-C18 fatty acid soap and soaps selected from lauric, oleic and other minor selected water soluble soaps. The level of sodium, potassium and magnesium are limited to 64%, 24% and 12%. This prior art is again directed to improvements in mildness, while maintaining acceptable lathering/sudsing, rinsing and processing characteristics.

It would be clearly apparent from the above that various combinations of personal cleansing bars are made available to the art involving combinations of soap and non- soap/synthetic surfactants. While mildness, lathering, processability etc. of formulations for cleansing bars are

usually targeted during the formulation of such cleansing composition, pH of the formulation is also associated with important product attributes such as stability and delivery of benefit agents, and maintenance of skin natural lipids.

US 5204014 discloses a low pH mild personal cleansing bar with lathering mild synthetic surfactants of about 20 to 50 %, and magnesium soap in amount of 5 to 50 %. The ratio of synthetic to Mg soap varied from 10: 1 to 0. 4 : 1 to obtain a pH in the range of 6.5 to 8. 5 in 1 % solution (25°C). This formulation although claims for a low pH bar clearly involves the use of synthetic detergents to control pH of soap, and also requires wax as an essential constituent.

While it is known that the use of synthetic surfactants as replacement for soap contributes towards lowering the pH values of cleansing bar compositions, random or widespread replacement of soap bars by syndet bars (synthetic detergent) has not so far been possible for a variety of reasons. This is primarily due to different physical characteristics of syndet bars as compared to soap bars such as for example smear or bar mushiness, lather and rinse quality.

Therefore, the above reveal the necessity of replacement of soap to the extent possible by synthetic detergents to lower the pH values of the soap, since it is usually not possible to achieve low pH formulations with only sodium soap since soap itself contributes towards the high pH of such formulations.

It is thus a basic object of the present invention to be able to provide for synergistic low pH cleansing compositions involving only soap and avoiding or minimizing the requirement of synthetic detergents in producing such low pH formulations.

Another object of the present invention is to be able to provide for synergistic low pH soap formulations with selective soap combinations which would enable obtaining low pH only soap based formulations, and in the process further achieve the advantageous benefit characteristics of soap formulations vis-a-vis its essential combinations with synthetic detergents to reduce pH as known in the art.

Yet further object of the present invention is directed to being able to identify possible soap based formulations which would on one hand enable maintaining desired bar properties of a soap formulation vis-à-vis synthetic detergents, and also facilitate incorporation of pH sensitive benefit agents in soap formulations thereby providing for a wider use/application of soap formulations.

Thus according to a firest aspect of the present invention there is provided a synergistic low pH cleansing composition comprising: i) 2 % to 30 % of soaps selected from sodium and potassium soap; ii) 30 % to 80 % of soaps selected from magnesium, calcium, zinc and aluminium soaps ; and iii) 4 % to 25 % water.

It is found by way of the invention that the above selective formulation, which includes basically only soaps and is free of synthetic detergents, by way of a synergistic and selective combination of the soaps selected from sodium and potassium soap along with the soaps selected from magnesium, calcium, zinc and aluminium soaps provides unexpectedly for a low pH soap formulation.

It is also found surprisingly by way of the invention that the presence of selective diluent such as free fatty acid in combination with the soaps selected from sodium, potassium, magnesium, calcium, zinc and aluminium soaps synergistically favours further lowering of the soap formulation's pH.

Thus according to another aspect of the invention, there is provided a low pH soap formulation comprising: soaps with or without synthetic detergents and other additives; and free fatty acid as a diluent in combination with at least one of the soaps selected from sodium, potassium, magnesium, calcium, zinc and aluminium soaps.

According to yet another aspect of the present invention, there is provided a synergistic low pH cleansing composition comprising: i) 2 % to 30 % soap selected from sodium and potassium soap; ii) 30 % to 80 % of soap selected from magnesium, calcium, zinc and aluminium soaps ; iii) up to 20 % free fatty acid ; and

iv) 4 % to 25 % water.

In accordance with yet a further aspect of the present invention, there is provided a process for the manufacture of low pH soap formulations comprising: i) providing 2 % to 30 % of soaps selected from sodium and potassium soap ; ii) providing 30 % to 80 % of soaps selected from magnesium, calcium, zinc and aluminium soaps; and iii) providing 4 % to 25 % water.

According to another aspect the process for the manufacture of the synergistic low pH soap formulation comprise: i) providing 2 % to 30 % soap selected from sodium and potassium soap; ii) providing 30 % to 80 % of soap selected from magnesium, calcium, zinc and aluminium soaps; iii) providing upto 20 % free fatty acid; and iv) providing 4 % to 25 % water.

The above formulations of the invention thus provide for low pH cleansing compositions involving only soap, and avoiding the requirement of synthetic detergents in producing such low pH formulations. In some embodiments, the compositions may be free (e. g. contain less than about 5 %, preferably less than about 3 %, preferably less than about 1 %, and ideally may be totally free) of synthetic surfactant. This would enable obtaining low pH only soap based formulations, and in the process further achieve the advantageous benefit

characteristics of soap formulation vis-a-vis its essential combinations with synthetic detergents to reduce pH as known in the art.

Importantly, the soap-based formulations would on the one hand enable maintaining desired bar properties of a soap formulation vis-a-vis synthetic detergents, and also facilitate incorporation of pH sensitive benefit agents in soap formulations, thereby providing for a wider use or application of soap formulations.

Importantly, the above selective low pH formulation is based on a surprising finding that sodium/potassium soap, which usually has a high pH value when selectively mixed with magnesium, calcium, zinc and aluminium soaps which have lower comparative pH value in combination is usually guided by the strongly alkaline sodium/potassium soap pH except at selective concentrations of the mix, which achieve a surprisingly lower pH for the combination. In fact, it is found that only for a selected concentration range the mix of sodium/potassium with magnesium/calcium/zinc/aluminium soap achieves a reduced pH, as otherwise even at lower and higher magnesium/calcium/zinc/aluminium (which is the soap having lower pH) concentration beyond the selected range the combination pH is determined principally by the high sodium/potassium pH values.

It is also a finding of the present invention that under dilution in the presence of free fatty acid the pH of sodium/potassium and magnesium/calcium/zinc/aluminium soaps can be surprisingly reduced even at less dilution.

Therefore, the invention and the formulation above provide for selective advantages of such surprising findings of possible lowering of pH of soaps by selective concentrations of soap mixes, and also in the presence of small amounts of free fatty acids as diluting agent.

Thus, it is possible by way of the above selective combination to achieve low pH formulations with only soap, with or without the use of additional synthetic detergent for further reduction in pH. The compositions of the invention can include other conventional additives such as polyethylene glycol, sorbitol, glycerine, and similar skin emollients and moisturising agents, in addition to skin- benefit agents like sunscreen, skin lightening, antibacterial agents and other pH sensitive additives.

As indicated above, the soap mix is selected from sodium or potassium soap in combination with soap selected from magnesium, calcium, zinc and aluminium.

In accordance with a preferred aspect of the invention, the soap formulation can involve addition of free fatty acid as a diluent, which synergistically favours obtaining soap based low pH formulations. The free fatty acid affects the lathering characteristics of the bars, and in particular surprisingly assists in lowering the pH levels of the formulation, apart from showing mildness improvement.

Advantageously the presence of such free fatty acid favours obtaining an emollient effect which tends to soften the skin, or otherwise improves feel on skin characteristics and scavenges any excess alkalinity.

Preferably, the free fatty acid suitable can be selected from stearic acid, hysteric acid, palmitic acid, myristric acid and lauric acid and mixtures thereof. It can preferably be present at a level of up to 20 %, conveniently 0. 1 % to 15 %, preferably 1 % to 12 %, optionally 5 % to 10 .

The formulation of the invention can optionally include synthetic detergent surfactants, which are typically selected from anionic, nonionic, amphoteric and zwetterionic synthetic detergents. Both low and high lathering/water solubility surfactants can be used along with suds boosting synthetic detergent surfactants as good dispersants.

EXAMPLES The details of the invention its objects and advantages are explained hereunder in greater detail in relation to non- limiting exemplary illustrations described hereunder.

Examples 1 to 12 Under these examples, the pH of sodium and magnesium soaps of varying concentrations individually and in combination was studied. For the purpose, following exemplary solutions of varying concentrations of sodium and magnesium soaps were obtained as detailed under Table I hereunder.

TABLE I Example Na Conc. Mg Conc. Na + Mg Conc. (%) 1:1 1 0. 25 %- 2-0. 25 %- 3--0. 25 % 4 0.5 % - - 5 - 0.5 % - 6--0. 5% 7 0. 75 %-- 8 - 0.75 % - 9 - - 0.75 % 10 1 % - - 11 - 1 % - 12 1 %

The pH values of the respective solutions under Examples 1 to 12 were plotted against the product concentration, as shown in figure 1.

As would be apparent from the figure 1, as the concentration of sodium soap was increased in solution, the pH rose steadily, and was always higher when compared to magnesium soap alone. In combination, a surprising and unexpected observation is apparent in that equimixture of sodium and magnesium soap does not necessarily provide for a throughout uniform mid-point of the sodium and magnesium soap pHs individually. The pH of the mixture is generally more towards the pH of the sodium soap, suggesting that sodium soap is a stronger alkali buffer.

However it was selectively identified that at a selective defined range of the combination, the pH is surprisingly lower than the rest of the trend. This according to the invention would enable selective reduction of pH of even only soap based formulations, without the need for synthetic detergents.

Examples 13 to 22 The following examples illustrates the effects of dilution of sodium soap using diluents such as sorbitol and free fatty acid. The concentration of the diluent effects of both sodium and magnesium salts in combination with FFA/Sorbitol were studied with concentrations of the solutions as detailed hereunder in Table II.

TABLE II Example Sorbitol+Na laurate Examples FFA+Na laurate 13 0. 0/1. 0180. 0/1. 0 14 0. 25/0.75 % 19 0. 25/0.75 % 15 0. 5/0.5 % 20 0. 5/0.5 % 16 0. 75/0.25 % 21 0. 75/0. 25 % 17 1. 0/0.0 % 22 1. 0/0.0 % The pH of the above diluted sodium salt of Examples 13 to 22 were noted, and compared with the pH of only sodium laurate.

The results are reproduced in accompanying figure 2A.

Examples 23 to 32

The following examples illustrate the effect of dilution of magnesium soap using diluents such as sorbitol and free fatty acid. The concentration of the diluent effects of magnesiumsalts in combination with FFA/Sorbitol was studied with concentrations of the solutions as detailed hereunder in Table III.

TABLE III Example Sorbitol+Mg laurate Examples FFA+Mg laurate 23 0. 0/1. 0 28 0. 0/1. 0 24 0. 25/0.75 % 29 0. 25/0. 75 % 25 0. 5/0. 5 % 30 0. 5/0. 5 % 26 0. 75/0.25 % 31 0. 75/0.25 % 27 1. 0/0.0 % 32 1. 0/0. 0 %- The pH of the above diluted magnesium salt of Examples 23 to 32 were noted, and compared with the pH of only magnesium laurate. The results are reproduced in accompanying figure 2B.

As would be evident from figures 2A and 2B under dilution, sodium and magnesium soaps reduce in pH, and more so at very dilute concentrations. There is no difference if diluted with water or humectants like sorbitol (in overall 1 % solution), suggesting that humectants do not play any significant role in bringing down the pH of either sodium or magnesium soap. However, in the presence of free fatty acid, it is surprisingly found that pH falls dramatically at even less diluent (small addition of FFA). The fall in pH is higher in case of magnesium soap as compared to sodium

soap, suggesting that the presence of magnesium helps to reduce pH faster with FFA, as compared to plain sodium soap alone.

Example 33 In order to ascertain the suitability of various soaps for low pH formulations, different soap solutions and their respective pH in solution were studied. For the purpose, solutions of sodium stearate, potassium stearate, calcium stearate, magnesium stearate, zinc stearate and aluminium stearate were studied. The pH of the respective salt solutions under varying concentrations of up to 10 % was noted. The results are represented in accompanying figure 3.

As evident from figure 3, it would be apparent that pH of potassium soap is found to be the highest, followed by the sodium. Importantly, zinc, magnesium, calcium and aluminium showed lower pH, and were found to be suitable for combining with sodium and potassium salt for obtaining low pH soap formulations.

Example 34 The dilution effect of the various cations in combination with selective FFA (stearic acid) at 10 % solution was next studied at various ratios of the stearate to the acid. The results in terms of variation in pH are noted as represented in accompanying figure 4.

As would be apparent from figure 4 the dilution effect of soap i. e. sodium and potassium soap were less as compared to the surprising dilution effects of the other cations i. e. magnesium, calcium, zinc and aluminium. Importantly, it is further apparent from the results in figure 4 that the selective cations magnesium, calcium, zinc and aluminium have surprisingly similar trends in pH reduction for dilution with FFA, and therefore can be advantageously combined selectively with sodium or potassium salts to obtain low pH only soap based formulations.

It is thus possible by way of the present invention to provide for low pH cleansing compositions involving only soap and avoiding the requirement of synthetic detergents in producing such low pH formulations. The selective formulation of the invention would enable obtaining low pH only soap based formulations, and in the process further achieve the advantageous benefit characteristics of soap formulations vis-a-vis its essential combinations with synthetic detergents to reduce pH as known in the art.

Importantly, the invention would on one hand enable maintaining desired advantageous bar properties of a soap formulation vis-a-vis synthetic detergents, and also facilitate incorporation of pH sensitive benefit agents in soap formulations, thereby providing for a wider use/application of soap formulations.