Regional variation in the free amino acids in the stratum corneum.

Regional differences in water-binding free amino acids (FAAs) in the stratum corneum (SC) may be expected, since differences in skin biophysical properties are well known. The objective was to determine whether differences in skin hydration as a function of body site may arise from differences in the chemical makeup of the skin, specifically the FAAs. Levels were quantified from serial SC samples collected from the forearm, calf, back, torso, and jaw in two studies using HPLC methods. FAA levels were higher from the calf versus the forearm and lower from the jaw compared to torso and back skin. Body site variations in skin hydration could not be attributed to differences in FAA levels.