Dark armpits may be caused by non-disease factors such as improper cleaning, and may be related to pathological factors such as acanthosis nigricans, post-inflammatory hyperpigmentation, and endocrine diseases. 1. Non-disease factors: such as improper cleaning of the armpits, long time without cleaning caused by the accumulation of local dirt, especially when the weather is hot and sweaty should be cleaned in time to improve the appearance. 2. Pathologic factors Acanthosis nigricans: mostly due to obesity, mostly seen in the armpits, the back of the neck and groin and other parts of the presence of folds, which can be manifested as deepening of the color of the skin to black, the surface there is a velvet-like thickening. Inflammation color: eczema, infection and other recovery, can stimulate the local melanocytes in the armpit, causing its function will be hyperactive, the synthesis of melanin increases, and further cause the armpit black. Endocrine diseases: such as hypoadrenocorticism can cause the axilla and other parts of the pigmentation, causing the axilla skin deepening black. Armpit black if the local cleaning symptoms did not change, it is recommended to go to the hospital to find out the cause of black armpit skin, clear diagnosis and active treatment, so as not to delay the condition.