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© 1998 Society of Cosmetic Chemists
Journal of the Society of Cosmetic Chemists, Vol. 49, No. 4, 257-273

An in vitro study of the effects of formulation variables and product structure on percutaneous absorption of lactic acid
A. Sah , S. Mukherjee , R. R. Wickett



The efficacy of lactic acid-containing products is linked to their ability to deliver it to specific skin strata. The penetration of L+ lactic acid to different skin layers of porcine skin from various emulsions was measured in vitro using flow-through diffusion cells. The effects of pH, propylene glycol, product structure, and mode of application on percutaneous absorption of lactic acid were investigated. The absorption of lactic acid from oil-in-water (o\/w) emulsions was measured at pH 3.8 and 7.0. The effect of propylene glycol (5%) as a penetration enhancer for lactic acid was also investigated from an o\/w emulsion. The emulsion was applied either as a finite-dose 2-μl topical film or as a 75-μl “infinite”-dose occluded patch on a 0.64-cm 2 skin disc. A key finding was that the effects of changes in product compositions such as vehicle pH and propylene glycol on percutaneous absorption of lactic acid depended on the application mode. Increasing the aqueous phase acidity in an oil-in-water emulsion enhanced lactic acid delivery in the finite dose but not in the infinite-dose application. Finite-dose films were significantly more efficient than infinite dose for lactic acid delivery to tissue compartments. The penetration enhancer propylene glycol was more efficacious at the infinite-dose application. However, it also significantly enhanced lactic acid delivery to viable epidermis in the finite-dose application. Finally, the effect of emulsion phase structure on lactic acid uptake was investigated by comparing delivery from oil-in-warer (o\/w), water-in-oil (w\/o), and water-in-oil-in-water (w\/o\/w) multiple emulsions with identical compositions. The total tissue delivery of lactic acid from the three emulsions was in the order of o\/w > w\/o\/w > w\/o.

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© 1998 Society of Cosmetic Chemists
Journal of the Society of Cosmetic Chemists