Dark armpits are considered to have adverse irritation, eczema, dermatitis, hyperpigmentation due to fungal infections, and may also be caused by acanthosis nigricans. It is recommended to reduce stimulation, apply topical ointment, and if necessary, with oral medication and physical therapy, which can make it white. 1. Undesirable stimulation: darkening of the armpit area is related to frequent friction, stimulation, sweating and other factors, resulting in local color darkening. It is recommended to pay attention to personal hygiene, reduce external stimuli, external hydroquinone cream, salicylic acid ointment continuously coated for a period of time, is conducive to improvement. 2. Eczema, dermatitis: armpit area has chronic skin diseases such as eczema, dermatitis, disease treatment leads to post-inflammatory hyperpigmentation, resulting in black color in the armpit. It is recommended to take good care of the local area and give vitamin E cream if necessary, which can be slowly recovered with the passage of time. 3. Fungal infection: fungal infection causes dermatophytosis, resulting in deepening of local pigmentation and blackening. It can be treated with topical ketoconazole and miconazole nitrate cream. 4. Acanthosis nigricans: the cause of acanthosis nigricans is not clear, and it is considered to be related to heredity, tumor, endocrine diseases, drugs and other factors. This disease occurs in the neck, armpit, groin and other places, resulting in local skin color gray-brown or gray-black. It is recommended to clarify the cause first and then treat it by drugs, laser or surgery. The black color of armpit persists, if necessary, go to the hospital, combined with the doctor’s advice to regulate the treatment.