WHY ARE THE PH LEVEL AND PRODUCT VEHICLE IMPORTANT IN COMPARING GLYCOLIC ACID SOLUTIONS?
Glycolic acid penetrates the stratum corneum in the free acid form. The neutralized, salt form does not immediately penetrate the skin, and depending on the type of salt (i.e. sodium glycolate) may never penetrate. The pH of a product determines the proportion of the total concentration of glycolic acid that is present as the acid form and the portion that is in the neutralized salt form. As a quick rule of thumb, any product formulated at pH 3.8 will have approximately half of its total glycolic acid content in the free acid form (i.e. an 8% glycolic acid product at pH 3.8 would contain 4% free acid). A product formulated at a lower pH will contain a higher amount of free acid, and will penetrate faster than a similar product having a higher pH. Product vehicle is important in maximizing product efficacy. Solutions tend to allow greater penetration than gel formulations, and gel formulations often require a higher pH to maintain stability thereby lowering available free acid. The NeoS
