There are small bumps under the armpits, which may be caused by folliculitis, sebaceous cysts, and dermatophytes. 1. Folliculitis: usually do not pay attention to personal hygiene, underarm sweaty moist easily induced bacterial infection, bacterial invasion of hair follicles caused by folliculitis, resulting in the appearance of localized small bumps. 2. Sebaceous cysts: underarm sebaceous glands are more, the secretion can not be normally discharged from the mouth of the hair follicle, in the local gathering to form cysts, resulting in the appearance of armpit pimples. 3. Skin lumps: also known as soft fibroma, is a common benign connective tissue tumor of the skin, belongs to the body surface superfluous organisms, mostly in middle-aged and old people. The etiology is unknown, and it is believed that it may be related to metabolic abnormalities such as elevated blood lipids and blood glucose, or caused by low-risk human papillomavirus infection, and the localization of underarms may show the manifestation of small meatballs. In addition, lipoma, fibroma, enlarged lymph nodes and so on are also the main reasons for the appearance of small bumps in the armpit. It is recommended to go to the dermatology department of the hospital to clarify the cause before treatment.