Without getting too technical, pH is a measurement referring to how acidic or alkaline a product is. The pH scale is numbered 1-14, with 1 being the most acidic and 14 being the most alkaline. Tap water is right in the middle of the scale, with an average pH of 7, which is considered pH-neutral. Given that AHAs and BHA exfoliate skin due to their acidic component, pH is critical to their performing as claimed or not offering much, if any, benefit to skin.
AHAs work best at concentrations of 5% to 10% with a pH of 3 to 4, and their effectiveness diminishes as you go above a pH of 4.5. BHA works best at concentrations of between 1% and 2%, and at an optimal pH of 3, diminishing in effectiveness as you go past a pH of 4. Both AHAs and BHA lose their effectiveness as a product’s pH goes up or the concentration of the ingredient goes down. (Sources: Dermatologic Surgery, February 2005, pages 149-154; and Cosmetic Dermatology, October 2001, pages 15-18.)
If the cosmetics industry isn’t forthcoming about the necessary percentages and pH for a BHA or AHA product (and most companies aren’t), how can you tell if it provides decent or effective exfoliation? Consumers can’t, not unless they are shopping with pH measuring paper in hand, which is exactly how I rate exfoliants when I review products for my book Don’t Go To The Cosmetics Counter Without Me, 7th Edition, and on my Web site at Beautypedia. com.
As a general rule, it is best if the AHA ingredient is either second or third on the ingredient list, making it likely that the product contains a 5% or higher concentration of AHAs. For salicylic acid, because only a 2% to 0.5% concentration is required, it is fine if this ingredient is located toward the middle or end of the ingredient list.
It is interesting to note that—at any pH—AHAs provide the added benefit of helping to keep water in the skin at the same time that exfoliation is taking place. This is due to the way they affect skin cells, which adds increased protection. AHAs can also increase the production of ceramides in the skin, which help keep it moist and healthy (Source: Dry Skin and Moisturizers: Chemistry and Function, edited by Marie Loden and Howard Maibach, 2000, page 237).
While BHA penetrates deeper into the pore than AHAs, it can be less irritating than AHAs. This is due to BHA’s chemical relation to aspirin. Aspirin (acetylsalicylic acid) has anti-inflammatory properties and so, on the skin, BHA (salicylic acid), which is derived from aspirin, retains some of its same anti-inflammatory benefits.
One more advantage that the BHA salicylic acid has for those struggling with acne it that it’s also mildly antibacterial. When an effective BHA product is combined with a potent topical disinfectant containing benzoyl peroxide, the 1-2 punch against bacteria improves your odds for successfully managing breakouts (Source: Steinberg, David C., Preservatives for Cosmetics, 2nd Edition, Allured Publishing, pages 39-40).