The reason for the blackening of the thigh root is many: 1. Obese people due to a large accumulation of fat in the armpits, the root of the leg part of the long-term friction local pigmentation, the body insulin secretion abnormalities lead to blackening of the thigh root, usually more exercise, control food intake to control weight growth can prevent this situation. 2. Pregnant women due to the body hormone levels rise, the body melanin increased resulting in the root of the thigh The skin is black and does not require special treatment, and the blackened skin on the thighs will gradually return to normal after the hormone levels in the body return to normal after the birth of the baby. 3, due to the dampness of the leg roots, a lot of sweating, and fungal infections that form ringworm for a long time without cure can also lead to blackened, rough, itchy, thickened skin on the leg roots. The skin color can gradually return to normal after the dermatitis is cured.