There are various factors for the darkening of the inner thigh skin, including pigmentation, increased sex hormones, friction and other common causes. In addition, local inflammatory reactions may also occur after the skin darkens. 1, pigmentation: inner thighs see little light, local sweating, humidity, and too tight bottoms lead to compression of blood flow in the inner thighs, thus causing melanin deposition, which is manifested as black skin, usually not accompanied by inflammatory changes such as erythema and papules, without conscious pain and itching; 2, increased sex hormones: sex hormone secretion Excessive, may stimulate the inner thigh skin, color change; 3, local inflammatory reaction: some patients have eczema on the inner thigh, after the inflammation subsides skin will leave melanin deposits; 4, friction: human armpits, inner thighs and other parts of the body, easy to occur skin friction, especially obese patients with small thigh skin gap, frequent friction easily cause blackening of the inner thigh. If there is only the phenomenon of black inner thighs, in general, no treatment is needed; if the endocrine abnormalities caused by obesity lead to black inner thighs, weight loss is required. Inner thighs do not sweat well, usually pay attention to washing, keep clean and dry.