Small painful bumps in the armpits may be caused by lymphadenitis, boils, paronychia, etc. 1. Lymphadenitis: Lymphadenitis may be caused by pathogens such as Staphylococcus aureus, Streptococcus b hemolyticus and other infections. Patients will have localized lymph node enlargement, pain and skin fever. If the patient has lymphadenitis in the armpit and the enlarged lymph nodes in the armpit form lumps, the manifestation of painful small bumps in the armpit will occur. 2. Boils: Boils are considered to be caused by pathogen infections such as yellow staphylococcus infection and staphylococcus epidermidis. Patients will have symptoms such as redness and swelling of the skin, heat and pain, yellow and white pus plugs, and small hard nodules. If the patient has boils in the armpits, he or she will have the symptom of growing small painful bumps. 3. Associate breasts: Associate breasts are mainly caused by congenital developmental abnormality, and patients will have swollen and bulging underarms or armpits, and some patients will have swelling and pain. If the patient’s armpit has paratits, it will be manifested as small lumps of pain in the armpit. It is recommended that patients with painful underarm bumps need to seek timely medical attention, and the doctor will treat them after clarifying the cause of the disease.