What does it mean if there is a painless lump under the armpit, and what should I do?
Dec 01, 2025
Source: Cainiu Health
Dr. Liu Wenmin
Introduction
In general, a painless lump under the arm may be caused by local friction, fat accumulation, sebaceous cysts, reactive lymph node hyperplasia, lipomas, or other reasons. It is recommended to seek medical attention promptly, identify the underlying cause, and then improve the condition through general measures or medication as directed by a doctor. In daily life, change clothes regularly, keep the underarm area dry, and avoid using harsh skincare or cleansing products.
Generally, a painless lump under the arm may result from local friction, fat accumulation, sebaceous cysts, reactive lymph node hyperplasia, lipomas, or other causes. It is recommended to seek medical attention promptly to determine the underlying cause and, under a doctor's guidance, improve the condition through general care, medication, or other treatments. Specific analyses are as follows:
1. Local friction: Wearing tight clothing frequently or repeatedly raising the arms can lead to repeated friction of the skin and subcutaneous tissues in the armpit area, gradually forming a firm, hardened mass. Immediately switch to loose, breathable cotton clothing, avoid tight contact with the armpit, reduce arm-raising movements, and apply a gentle moisturizing lotion after daily cleansing to protect the skin barrier.
2. Fat accumulation: Long-term high-calorie diet combined with lack of physical activity may cause abnormal fat buildup in the armpit, forming firm nodules that feel smooth and are not tender upon touch. Adjust dietary habits by reducing intake of fried foods and sweets, engage in 30 minutes of aerobic exercise daily, and combine with localized massage of the armpit area to promote fat metabolism and blood circulation.
3. Sebaceous cyst: Blockage of sebaceous gland ducts in the armpit leads to retention of sebum and formation of a cyst, presenting as a round, firm lump without significant pain. Keep the armpit clean and dry, avoid squeezing or irritating the cyst. If signs of infection occur, follow medical advice to use topical medications such as mupirocin ointment, fusidic acid cream, or compound polymyxin B ointment.
4. Reactive lymph node hyperplasia: Infections in areas such as the mouth or throat may spread to the axillary lymph nodes, causing them to swell and harden, often without pain initially. Actively treat the primary infection and, as directed by a physician, use antibiotics such as cefaclor capsules, amoxicillin-clavulanate potassium tablets, or roxithromycin capsules. Once the infection is controlled, the lump typically shrinks gradually.
5. Lipoma: A benign overgrowth of fatty tissue forms a soft-firm mass with clear boundaries and slow growth. If the lump is small and asymptomatic, regular observation is sufficient. If it affects daily life or continues to grow, surgical excision (lipoma removal) may be performed to completely remove the tumor and prevent recurrence.
In daily life, change clothes regularly, keep the armpits dry, and avoid using harsh skincare or cleansing products. Maintain a light diet, eat more fresh fruits and vegetables to supplement vitamins, and establish regular sleep patterns to boost immunity. Avoid vigorous scrubbing of the lump during bathing, and practice scientific self-care to reduce the risk of complications.
