The difference between alpha hydroxy acids and beta hydroxy acids are their lipid solubility. Alpha hydroxy acids are water soluble and beta hydroxy acids are oil soluble. So I would treat a client with acne, whiteheads & blackheads with a beta hydroxy acid (salicylic) because it would penetrate the pore dissolving the oil and exfoliating the dead skin cells that are built up in the pore. I would treat a client with an alpha hydroxy acid (glycolic) that has thick, sun damaged, hyper-pigmentation, superficial wrinkles and where breakouts are not a problem.
Alpha hydroxy acids
Glycolic acid - derived from sugar canes
Lactic acid - derived from milk
Malic acid - derived from apples and pears
Citric acid - derived oranges and lemons
Tartaric acid - derived from grapes
Kojic acid- derived from maltic rice
Beta hydroxy acid
Salicylic acid - willow tree