Hydroxycarboxylic acids, N-acetylamino sugars, and N-acetylamino acids.

Most alpha-hydroxyacids and polyhydroxy acids are physiologic, natural, and nontoxic substances. All members of the group promote normal keratinization and desquamation. Those with multiple hydroxyl groups are moisturizing antioxidants, and are especially gentle for sensitive skin. Alpha-hydroxyacids and polyhydroxy acids can increase biosynthesis of glycosaminoglycans and collagen fibers, and cause substantial skin plumping and increased dermal thickness. Formulation of alpha-hydroxyacids and polyhydroxy acids in combination with pharmaceutical agents can enhance efficacy and diminish or eliminate side effects and drug resistance. N-acetylamino sugars and N-acetylamino acids are two other categories of physiologic substances that can: 1) increase skin thickness; 2) improve wrinkles and photoaged skin; and 3) eradicate itch in senile and eczematous dermatitis.