The surface of the healthy skin in adults is not uniformly acid. Some zones have a higher acidity than others, and in a few areas where surfaces are in apposition (intertriginous, interdigital, axillary spaces) the reaction may approach neutrality or even alkalinity.*
The presence of these nonacid zones within the physiologic "acid mantle" of the skin has recently become of pediatric interest. Herrmann, Behrendt, and Karp8 observed in the course of dermatologic investigations that the skin pH pattern in children differs from that of adults mainly by the absence of the "alkaline" reaction in the axillary pits. During childhood, up to about 10 years, the axillary skin pH was found to be more or less acid; but in the older age groups it rose progressively towards the neutral or alkaline values commonly encountered in adults. This increment of pH was regarded as a sign of beginning adolescence, indicating development
BEHRENDT H, GREEN M. The Relationship of Skin pH Pattern to Sexual Maturation in Boys. AMA Am J Dis Child. 1955;90(2):164–172. doi:10.1001/archpedi.1955.04030010166006
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