If your underarm skin discoloration is actually hair showing through your skin, having the hair removed by a cosmetic waxing procedure will probably take care of the visible darkening.
If you suspect that dead skin buildup is the culprit, talk to a dermatologist. He or she can diagnose the condition and prescribe a strong exfoliant that will remove the dead skin without irritating healthy skin. Remember that this can take several weeks. Contact your dermatologist if the dark skin itches or becomes inflamed -- these could be signs of an allergy to the treatment or an infection [source: Cosmopolitan].
If your skin is discolored because stimulated melanocytes are producing extra melanin, the treatment process is more involved. You need to prevent the melanocytes from making more melanin, so you'll have to see a dermatologist. He or she may prescribe a topical ointment that contains hydroquinone, an ingredient that blocks one of the steps in melanin production. It's safe to use on a short-term basis in low- to medium-strength formulas, but it's not recommended for long-term use [source: Todorov]. Topical creams that contain alpha hydroxy acids are also often prescribed to treat this condition because the acids help remove old cells [source: Todorov].
If you know you're susceptible to darker skin caused by melanin overproduction, avoid irritating your skin. Don't use harsh hair-removal techniques, such as waxing or plucking, and try using a deodorant or antiperspirant that's designed for sensitive skin [source: Skincare-news].
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