Finding a lump in your armpit, medically known as the axilla, can be a concerning discovery. The armpit is a complex region containing skin, fat, sweat glands, hair follicles, and a concentration of lymph nodes. All these structures can develop various types of growths. While the presence of a bump often triggers anxiety, most armpit lumps are benign and result from common, minor issues. Understanding the potential origins of these lumps, from superficial skin problems to deep immune system responses, can help demystify the finding and guide your next steps.
Localized Skin and Tissue Causes
Many armpit bumps originate from the skin and structures directly beneath it, often relating to hair removal or blocked glands. Ingrown hairs are a frequent cause, occurring when a hair strand, often after shaving or waxing, curls back and grows into the skin instead of out of the follicle. This creates a small, red, sometimes painful bump that may contain pus, resembling a pimple or small cyst. These localized bumps are usually isolated and often resolve naturally within a few days or weeks as the hair works its way out.
Another common type of benign lump is a cyst, such as an epidermal inclusion cyst, which forms when surface skin cells move deeper and multiply, creating a sac filled with keratin. These cysts are typically slow-growing, soft or firm, and can be easily moved under the skin. Less frequently, a lipoma may be the cause, presenting as a soft, doughy lump composed of fatty tissue situated deeper beneath the skin. Lipomas are generally painless and highly movable, making them one of the most identifiable non-cancerous growths.
Understanding Swollen Lymph Nodes
The most frequent cause of a noticeable armpit bump is the enlargement of the axillary lymph nodes, a condition called lymphadenopathy. Lymph nodes are small, bean-shaped structures that function as filters within the lymphatic system, trapping and destroying foreign substances like bacteria, viruses, and abnormal cells. The armpit contains a significant cluster of these nodes, which drain lymph fluid from the arm, chest wall, and breast.
When the body detects an infection or inflammation in the upper body, the lymph nodes begin producing a large number of infection-fighting white blood cells. This rapid increase in immune cell production causes the nodes to swell, often to the size of a pea or a grape, becoming tender and sometimes painful to the touch. Common triggers include a localized skin infection on the hand or arm, a common cold, the flu, or even a recent vaccination, such as a COVID-19 or flu shot.
Reactive swelling is a sign that your immune system is functioning correctly, actively responding to a threat. These temporarily enlarged lymph nodes are typically soft and movable. They should decrease in size as the underlying infection or inflammation resolves, usually subsiding within a few weeks.
When the Bump Signals Serious Health Concerns
While most armpit lumps are temporary or benign, a small percentage can indicate a more serious underlying health issue. The primary concern is malignancy, which includes cancers that originate elsewhere and spread to the lymph nodes, or cancers of the lymphatic system itself. The axillary lymph nodes are particularly relevant in the diagnosis and staging of breast cancer, as they drain approximately 75% of the lymph from the breast tissue.
A lump that is cancerous often presents with distinct characteristics. These lumps tend to be hard, irregular in shape, and fixed or immobile because they are anchored to surrounding tissue. Unlike the painful, tender swelling of a temporary infection, cancerous lumps are sometimes painless, though pain is not a reliable way to rule out malignancy.
Chronic inflammatory skin conditions, such as Hidradenitis Suppurativa (HS), can also manifest as persistent, deep, and painful lumps in the armpit. HS involves chronic inflammation and blockages of the hair follicles, leading to recurring abscesses, tunnels under the skin, and significant scarring. This chronic disease requires specialized medical management and should not be mistaken for a simple ingrown hair.
Determining When to See a Doctor
Seeking professional medical evaluation is necessary for any armpit lump that causes concern or does not fit the profile of a minor, temporary issue. Consult a healthcare provider if the lump persists for longer than two to four weeks without shrinking. A provider should also examine any lump that rapidly increases in size or feels unusually hard, firm, or fixed in place, especially if it cannot be easily moved under the skin.
Immediate medical attention is warranted if the lump is accompanied by other systemic symptoms that suggest a broader illness. Additionally, any changes to the skin overlying the lump, such as redness, warmth, or dimpling, should prompt a consultation.
Warning Signs
These systemic warning signs include:
- Unexplained fever
- Drenching night sweats
- Unintentional weight loss