Skin Exfoliation: Does Pain Equal Gain? The Science behind this Question: by Dr. Diana Howard Lactic acid and glycolic acid are the front-runners in the world of alpha hydroxy acid (AHA) exfoliation. So, which ingredient works best to reveal a newer, fresher you? Independent research studies on AHAs have determined that: Glycolic acid, the smaller molecule of the two, penetrates the skin more readily than…