A lump in the armpit, or axillary region, is a common finding. This area contains skin, fat, sweat glands, hair follicles, and a dense network of lymph nodes. Because of this variety of structures, lumps can arise from many different causes, ranging from temporary immune reactions to chronic conditions or growths. While most armpit lumps are benign and resolve on their own, any sudden or persistent change warrants careful attention.
Understanding Acute Swelling From Lymph Nodes and Skin Irritations
The most frequent cause of a noticeable lump is the enlargement of a lymph node, known as lymphadenopathy. Lymph nodes function as filters within the lymphatic system, trapping foreign particles, bacteria, and virus-infected cells. When the body detects infection or inflammation in the upper extremities, chest, or breast, the regional axillary nodes swell as they process these elements.
This acute swelling indicates the immune system is active, often in response to a common cold, flu, or a localized infection. Reactive lymph nodes are typically tender, mobile, and feel like a small, firm, bean-shaped structure. They usually decrease in size and disappear once the underlying infection has cleared.
Skin irritations are another common source of acute lumps, particularly in an area frequently subjected to hair removal and product use. Folliculitis (inflammation of a hair follicle) and ingrown hairs can create tender, red bumps resembling small boils. These minor infections occur when bacteria enter the damaged follicle, leading to a localized collection of pus.
An epidermal inclusion cyst (sebaceous cyst) is a non-cancerous sac that develops when a hair follicle becomes blocked. While stable, these cysts may become infected and inflamed, causing sudden, painful swelling. Allergic reactions to deodorants, antiperspirants, or soaps can also trigger localized irritation and swelling, often accompanied by redness or itching.
Chronic Inflammatory Skin Conditions Specific to the Armpit
Some armpit lumps are manifestations of chronic dermatological issues requiring long-term management, rather than temporary reactions. Hidradenitis Suppurativa (HS), also called acne inversa, is a recurring inflammatory skin disease targeting areas where skin rubs together, including the axilla. HS begins with painful, deep nodules that form under the skin due to blocked hair follicles.
These lumps can persist for weeks or months, often rupturing to drain pus and fluid. Advanced HS is distinguished by the formation of sinus tracts, which are tunnel-like passages connecting the lumps beneath the skin. Repeated cycles of inflammation and healing can lead to characteristic scarring.
HS is a chronic condition that recurs and requires specific medical treatment, unlike acute boils. While the exact cause is not fully understood, it involves a combination of genetic, hormonal, and environmental factors, not poor hygiene. The chronic nature and deep tracts differentiate HS lumps from temporary acute swelling.
Recognizing Non-Infectious Growths and Tumors
Lumps not caused by infection or inflammation often represent solid masses, which can be benign soft tissue growths or, less commonly, malignant tumors. A lipoma is a common benign growth consisting entirely of fat cells, found just beneath the skin’s surface. Lipomas typically feel soft, doughy, and movable when pressed, growing slowly over time.
These fatty tumors are generally painless, though a large lipoma can cause discomfort if it presses against a nerve or restricts movement. They are harmless and do not turn into cancer. Fibroadenomas, which are non-cancerous lumps of glandular and fibrous tissue, can also be felt in the armpit if they are an extension of breast tissue.
Malignant lumps are much rarer and present with different characteristics. Cancers such as lymphoma or metastatic breast cancer spread to the axillary lymph nodes, can cause lumps. These lumps are more likely to be firm or hard, fixed to the underlying tissue, and may be painless. Any lump that is rapidly growing, hard, or immobile requires prompt investigation.
Guidance on Medical Evaluation and Red Flags
Because the armpit contains many different tissue types, a professional medical evaluation is necessary to accurately determine the cause of any persistent lump. The first step is a physical examination, where a doctor assesses the lump’s size, texture, mobility, and tenderness. This often allows the doctor to differentiate between a soft lipoma, a mobile lymph node, and a fixed, harder mass.
Red Flags for Urgent Evaluation
There are specific symptoms that indicate a need for urgent medical attention. You should see a doctor immediately if a lump is rock-hard, fixed to the tissue, or rapidly increasing in size over weeks. Other concerning signs include a lump that persists for more than two weeks without an obvious cause, or one accompanied by systemic symptoms. Systemic red flags include unexplained weight loss, persistent fever, or drenching night sweats, which can suggest conditions like lymphoma. Depending on the physical exam findings, a doctor may order further testing, such as an ultrasound to determine the lump’s composition, or a biopsy for a definitive diagnosis.