Underarm melanosis may be caused by physiological factors such as excessive friction, or it may be caused by post-inflammatory hyperpigmentation, acanthosis nigricans and other diseases, and it can be improved through general treatment, medication and other ways. 1. Physiological factors: If the underarm melanosis is caused by excessive friction, it usually does not need special treatment. Wear loose clothing and reduce friction. 2. Post-inflammatory hyperpigmentation: underarm hyperpigmentation may also be post-inflammatory hyperpigmentation, patients can follow the doctor’s instructions for local topical azelaic acid, hydroquinone cream and other drugs, which can inhibit melanin production and improve hyperpigmentation. 3. Acanthosis nigricans: Acanthosis nigricans can also lead to underarm hyperpigmentation, patients should pay attention to diet and exercise. You can use hydroquinone cream, cod liver oil ointment and other drugs as prescribed by the doctor, which can moisturize the skin and reduce hyperpigmentation. For people with melanosis under the armpit, after excluding physiological factors, it is recommended to go to a regular hospital, under the guidance of the doctor for treatment.