Both AHA and BHA are ingredients of active skincare products. The most popular alpha hydroxy acids are exfoliants that are glycolic acid, which is produced from sugar cane and lactic acid which is derived from milk. The only one beta hydroxy acid used in skincare is salicylic acid.
The main difference between alpha hydroxy acids and beta hydroxy acid is their oil solubility. While AHA (alpha-hydroxy acids) are water-soluble, BHA (beta hydroxy acid) is oil soluble. This means that beta hydroxy acid is able to penetrate into the pore, which contains sebum, and exfoliates the dead skin cells that build up inside the pore.
Due to this difference in properties, beta hydroxy acid is better used on oily skin with blackheads and whiteheads. Alpha hydroxy acids are better used on aged, thickened, sun-damaged skin where breakouts are not a problem. Salicylic acid (BHA), causes the cells of the epidermis (the outermost layer of the skin) to become "unglued," allowing the dead skin cells to slough off, unclogging the openings of the skin pores. Applied daily for at least 6 months, salicylic acid can also is reported to improve post acne brown spots.