Healthy skin consists of dead, hardened skin cells, which are surrounded by water, various lipids, oils, acids, and salts. This hydrolipic layer is also known as the acid shield because of its low pH, and it forms a natural protective outer skin, which is flexible, keeps out micro organisms and dangerous substances, reduces physical damage, and retains moisture. When water comes into contact with skin the components of this layer disintegrate. This process is accelerated, when the water is warm, contains detergents, and when there is prolonged exposure. Such washed out skin distends and loses its natural biological and physical protective function.

During the washing process of skin, individual components of the hydrolipic layer are dissolved. This process is accelerated by the use of warm water and cleansing agents, regardless of whether acid, alkaline, or neutral soaps are used. Because of the dissolved hydrolipic layer, the skin loses a considerable part of its protective function. The regeneration of the hydrolipic layer must be accomplished by the skin itself rather than by external means, in order to be biologically effective. Skin care lotions are therefore designed and intended to encourage and support the regeneration process of the skin.