Black pimples on armpits are blackheads which is a type of acne and can be treated by general treatment, topical medication, systemic medication, phototherapy and other methods. 1. General treatment: keep the skin clean, avoid squeezing and scratching, eat less high-sugar, greasy food, avoid staying up late. 2. Topical medication: Commonly used medications include Vitamin A acid cream, benzoyl peroxide gel and other medications. 3. Systemic medication: you can take isotretinoin, minocycline, doxycycline and so on. 4. Phototherapy: using LED blue light or red light irradiation, you can also take photodynamic therapy and other measures. It is recommended to go to the hospital for examination first and follow the doctor’s instructions for treatment.