Salicylic Acid
Also called beta hydroxy acid (BHA), this multifunctional ingredient addresses many of the systemic causes of acne. Its primary benefit is as an exfoliant, helping shed dead skin in a way similar to how skin acts when we are younger. Because it has the ability to penetrate into the pore lining and exfoliate inside the pore as well as on the surface of skin, it is especially effective for reducing breakouts, including blackheads and whiteheads.
In addition to these benefits, salicylic acid also has soothing properties to calm aggravated skin, can help minimize the appearance of an uneven skin tone, and has hydrating abilities that can result in smoother skin.
Paulas Choice, Expert Advice Ingredient Dictionary, Salicylic Acid, 2017
Lactic acid
Alpha hydroxy acid (AHA) extracted from milk, although most forms used in cosmetics are synthetic because that form is easier to formulate with and stabilize.
In a pH-correct formula (generally a product would have a pH between 3 and 4) and in concentrations between 5 and 12%, lactic acid exfoliates on the surface of skin by breaking down the material that holds dead skin together, allowing it to shed naturally as it once did. Lactic acid may cause sensitivity, although this isn’t common and can be minimized, if not eliminated, if the formulation contains soothing ingredients.
Lactic acid also has hydrating properties and, like glycolic acid (another AHA), helps brighten an uneven skin tone.
Paulas Choice, Expert Advice Ingredient Dictionary, Lactic Acid, 2016
