There are many reasons why women’s armpits are dark, the most common being pseudo acanthosis nigricans, post-pregnancy hyperpigmentation, red ringworm and the possibility of ringworm. Pseudo acanthosis nigricans is related to obesity, and in addition to the darkening of the armpits the other folds of the body can become dark and accompanied by a skin rash, and most of the rashes can naturally subside after correcting the body weight. After pregnancy, the level of melanin-stimulating hormone in the body will increase, and diffuse hyperpigmentation may appear in the armpits, umbilicus, genitals, areola and other parts of the body, which belongs to the normal physiological phenomenon, and can be relieved naturally after delivery. Tinea corporis is a skin infection caused by the bacterium Clostridium perfringens, which is mainly characterized by the appearance of brown or dark red patches with dandruff in the armpits. Tinea corporis may cause darkening of the skin in the armpit area, which is caused by fungal infections, and is mostly seen in patients with excessive sweating in the armpit area.