Skin can darken for all sorts of reasons: Sun exposure, scarring and a host of dermatological disorders can all affect skin tone. But there are several factors that can contribute to dark skin under your armpits, and they range from serious medical conditions to simple problems that can be corrected with minor behavioral changes.
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The American Osteopathic College of Dermatology identifies acanthosis nigricans as a disorder recognized by the dark markings it leaves under the armpits, around the groin and on the neck. The dark patches are abnormal skin growths that appear as a result of elevated insulin levels, and usually indicate insulin resistance, which is a major risk factor for type-II diabetes. Acanthosis nigricans is most common among obese people, but the Mayo Clinic reports that other causes may include the use of oral contraceptives, high niacin levels, hormone disorders, endocrine disorders, tumors and some types of cancer. The underlying condition must be corrected in order to make the darkening under the armpit go away, but the areas can be cosmetically treated with skin lightening creams.
Another skin condition identified by the American Osteopathic College of Dermatology, hyperpigmentation, may also cause dark patches of skin under the armpits. This condition, however, does not disproportionately affect the underarms compared to other areas of the body. Hyperpigmentation is fairly common and usually harmless, and creates dark skin through excessive melanin production. Over-the-counter and doctor prescribed skin lightening creams can reduce the appearance of hyperpigmentation, and other relevant therapies include chemical peels and laser treatments.
Uric Acid Stains
The Health and Beauty site Daily Glow states that excessive sweating is among the most common causes of dark underarm skin, because sweat contains a natural enzyme called uric acid. With repeated, prolonged exposure, uric acid can darken skin, so routine bathing and use of high-quality antiperspirants are important steps in the prevention of discoloration.
When armpit skin becomes irritated due to friction from shaving or abrasive clothing, it can turn brown or gray, according to Cosmopolitan Magazine. To avoid this irritation, wear non-irritating fabrics like cotton in layers beneath scratchy fabrics like wool or restrictive ones like tight polyester. Also, replace shaving razor blades regularly, use shaving cream and thoroughly rinse shaving blades after every stroke.
Dead Skin Cells
The beauty tip website The Beauty Brains indicates that dead skin cells can accumulate in the uneven crevices of armpit skin, which may give it a dark appearance. Routine exfoliation, ideally with a lactic acid exfoliating cream, will help clear up darkness related to this cause.
The Beauty Brains also explains that armpit hair can create the impression of dark skin if the hair is naturally darker than the skin tone. Even with regular shaving, hairs may be visible at or just below the skin level. Waxing in lieu of shaving can extract these hairs at the root, giving underarms a lighter appearance.