ABSTRACT
HYDROXYACIDS: BIOAVAILABILITY AND BIOAVAILABLE CONCENTRATION Stratum Corneum Barrier In normal human skin, the stratum corneum consists of 14 to 30 layers of corneocytes including the inner level stratum compactum and the outer level stratum dysjunctum. The keratinenriched corneocytes in the stratum corneum are embedded in a lipid matrix and are very resistant to penetration by ionic compounds or large molecules with molecular weight greater than 800 to 1000. While undissociated glycolic acid or lactic acid molecules can readily penetrate into the stratum corneum, the ionized glycolate or lactate anions from the metallic salt cannot. Although the active form of a hydroxyacid may be the anions once inside the skin, a topical formulation must contain a bioavailable form which can penetrate into and through the stratum corneum.
