AHA (alpha-hydroxy acid) is a fruit acid and is found in glycolic-, mandelic- and lactic acid, for example. It is particularly gentle on impure skin, scars, wrinkles, clogged pores and hyperpigmentation. Tip: approach the application slowly by starting with a dosage of 2 percent, then gradually increase it to 10 percent. AHA is particularly beneficial for dry and sensitive skin. A high level of sun protection is important during the day.