To obtain a safe skin cosmetic not causing milk allergy, even after used for a long period, and having a moisture-retaining cuticle protection effect, a beautifully whitening effect, and a refreshing use touch.

Lactose in a whey is decomposed, and the left whey is treated with a bread yeast, Saccharomyces cerevisiae, and subsequently thermally treated to inactivate the yeast. Lactoglobulin and lactoalbumin are further removed as denatured proteins. The obtained whey (lactoskin) containing protein type nitrogen compounds and soluble lipids is added to a skin cosmetic.