A phenol peel, which is the strongest chemical peel, treats deeper skin problems such as coarse facial wrinkles and precancerous growths, as well as areas of blotchy or damaged skin caused by sun exposure, aging or birth-control pills. Because phenol can lighten skin where it is applied, the patient's natural pigmentation is a factor in determining a phenol peel's suitability. Phenol is used only on the face because it may cause scarring elsewhere. Full-facial treatment can last an hour or two, and recovery can take a few months, with possible permanent lightening of the skin and removal of freckles.