Not all acids are created equal. It is important to know the four factors which can impact how an acid affects the skin. The four factors are chirality, pH, percentage, and base.
The science of chirality has an impact on how ingredients affect the skin. Chirality is a chemical process that takes the ingredient from its natural state and improves it by mirroring the more perfect side of the molecule. Think of it like handedness. When an ingredient has been chirally corrected the efficacy, strength, and purity is increased. To identify chirally corrected ingredients, look for the singular letter L, D, or R in front of or behind the ingredient name ie. L-Lactic Acid or Lactic Acid (L).
The pH of an acid affects how it penetrates through the acid mantel of the skin and into the epidermal layers. Healthy skin has a normal pH of 5.5 and acid formulations may range from a 3.0 or less. The lower the pH means the difference in an acids strength and how it will react with the skin.
Percentage of an acid is also important; however, how it reacts on the skin will also depend on the pH. You can have a 70% glycolic acid with a high pH and a 20% glycolic with a low pH and they will affect the skin differently. The 20% glycolic with the lower pH will penetrate the acid mantel and epidermal levels, creating a change in the skin.
What type of base the acid is in has an impact on how it will perform on the skin. Acids in a cream base will be more concentrated to the stratum corneum, versus an acid in a polymer base which will allow for more even penetration into the epidermal layers, thus creating a more even peel throughout.