The roles of pH and concentration in lactic acid-induced stimulation of epidermal turnover.
BACKGROUND
Alpha hydroxy acids such as lactic and glycolic acids (AHAs) accelerate epidermal turnover and exfoliate the stratum corneum. The roles of pH and concentration in these antiaging effects of AHAs is unclear, but a lower (more acidic) pH and higher concentration of acid are thought to be more effective.


OBJECTIVE
To examine the effects on skin renewal rates of lactic acid 10% at pHs of 2.0, 3.0, and 4.0, and of 5%, 10% and 15% lactic acid at a pH of 3.0.


METHODS
Twenty-six female subjects participated in the double-blind, randomized, placebo-controlled study. The dansyl chloride stain technique was used to measure epidermal renewal times.


RESULTS
Both pH and concentration are critical in the lactic acid effect. At a fixed lactic acid concentration, the desquamative effect was highly pH dependent. At a fixed pH, the turnover rate of skin was concentration dependent.


CONCLUSIONS
The desquamative and proliferation-stimulating effects of lactic acid are very pH and concentration dependent, suggesting the "free acid" concentration is the active moiety.
Thueson
D O
DO
Cosmederm Technologies, Inc., La Jolla, CA 92037, USA.
Chan
E K
EK
Oechsli
L M
LM
Hahn
G S
GS
D000328:Adult; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D004817:Epidermis / Q000378:metabolism*; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007641:Keratolytic Agents / Q000008:administration & dosage* / Q000494:pharmacology*; D019344:Lactic Acid / Q000008:administration & dosage / Q000494:pharmacology; D008875:Middle Aged; D012016:Reference Values; D016896:Treatment Outcome
D007641:Keratolytic Agents; D019344:Lactic Acid