Brief Answer: Inflammed gland... Detailed Answer: Hi, Hair follicles, sweat glands and lymph nodes under the arm might be inflammed giving rise to painful swelling under the arm. Some times the swelling can grow into abscess that needs to be drained under aseptic precautions especially Ibuprofen can be continued twice a day for few more days to reduce pain. You may also use topical antibiotics such as neosporin on the affected area. It will provide you some benefits. I would also recommend that you visit a surgeon or physician nearby to assess the condition. He/she can guide you with antibiotic drugs or choose to perform incision and drainage. Hope this helps. Let me know if you need clarifications. Regards

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