To produce a sheet-formed cosmetic useful for preventing the aging of the skin by effectively utilizing the shell of an egg such as hen's egg and forming the shell in the form of a sheet.

A water-soluble shell membrane produced by the treatment of a shell membrane of an avian egg with an acid, alkali, oxidizing agent, reducing agent, enzyme, etc., is used in the form of a sheet. The cosmetic material can be produced e.g. by forming a sheet from the soluble shell membrane or a mixture of the shell membrane with an excipient, etc., or applying the soluble shell membrane to the surface of a sheet material other than the shell membrane by lamination, coating, etc. Especially the latter cosmetic material is preferable owing to its high strength, etc. The other sheet material to be used in the above process as a substrate is e.g. a flexible sheet material such as polyethylene or polyvinyl alcohol or a woven cloth made of silk, rayon, polyester, polyurethane, etc. The sheet cosmetic is brought into close contact with the face, abdomen, back, etc., for 5-60 minutes and the operation is performed at a frequency of thrice a week for ≥1 month to attain a good effect.