The armpit, or axilla, is a complex anatomical space that often causes anxiety when a lump is discovered. This region is densely packed with soft tissue structures, including blood vessels, nerves, sweat glands, and the axillary lymph nodes. These nodes, which number between 20 and 49, function as filters for the lymphatic fluid draining from the upper limb, chest wall, and breast tissue. While most lumps are benign, the axilla is an important location where malignant disease can manifest, often due to the nodes reacting to disease elsewhere in the body.
Why Armpit Lumps Are So Common
The vast majority of lumps found in the axilla are not malignant. The most frequent cause of swelling is lymphadenopathy, the enlargement of the lymph nodes as they filter infectious agents. These nodes commonly swell in response to bacterial or viral infections, such as the common cold or a localized infection from a scratch.
Skin irritation and inflammation frequently lead to the formation of small, often painful lumps. Folliculitis, caused by shaving or waxing, can result in localized swelling. Allergic reactions to hygiene products like soaps and deodorants can also cause temporary lymph node swelling.
Other benign masses originate directly from the surrounding soft tissue. These include lipomas (harmless, non-tender fatty growths) and cysts (sacs filled with fluid or pus beneath the skin’s surface). Hidradenitis suppurativa, a chronic inflammatory skin condition, can also cause painful, deep lumps and abscesses.
Routine vaccinations can temporarily cause lymph nodes to swell as the immune system mounts a response. In all these common scenarios, the lump is usually tender, mobile, and resolves on its own within a few weeks.
Cancers That Manifest in the Axilla
The axilla is most often involved as a site of secondary disease, meaning cancer that has spread from another location. The most common malignancy is breast cancer, as lymphatic drainage flows directly into the armpit nodes, making them the primary destination for traveling cancer cells. About 40 to 50 percent of individuals diagnosed with breast cancer show involvement of these nodes, which significantly impacts staging and subsequent treatment.
The axilla is also a location where cancers of the lymphatic system, known as lymphomas, can originate. Lymphomas, including Hodgkin’s and Non-Hodgkin’s types, involve the uncontrolled growth of white blood cells within the lymph nodes. In these cases, the lymph node swelling is the primary manifestation of the disease.
Other cancers can also metastasize to the armpit. Malignant melanoma can spread from a primary site on the upper extremity or chest wall to the regional axillary nodes. Less often, cancers originating in distant organs, such as the lung or thyroid, may use the lymphatic network to reach the axilla.
Critical Warning Signs Requiring Doctor Visit
Certain characteristics of an armpit lump warrant prompt medical attention. The persistence of a lump is a concern; any swelling that does not shrink or resolve after two to four weeks needs professional evaluation. Malignant masses often feel hard, firm, or rock-like in texture. Unlike soft, mobile nodes associated with infection, a suspicious lump may be fixed or tethered to the underlying tissue.
The appearance of systemic symptoms accompanying the lump should also raise concern. These generalized symptoms, sometimes called B symptoms, are particularly relevant to lymphoma. They include persistent, unexplained fever, drenching night sweats, and significant, unintentional weight loss.
Other concerning physical findings include changes to the skin overlying the lump, such as redness, scaling, or dimpling. Any sudden, continuous increase in the size of the lump requires immediate medical review. A healthcare provider will typically perform a physical exam and may recommend imaging studies to determine the lump’s nature.
Factors That Increase Your Cancer Risk
A person’s risk of developing cancers that affect the axilla is influenced by genetic and lifestyle factors. Advancing age is a consistent risk factor, with the likelihood of a malignant cause increasing significantly after age 50.
Genetic predisposition plays a significant role, particularly inherited changes in genes like BRCA1 and BRCA2, which increase the lifetime risk for breast and ovarian cancer. A family history of breast cancer in a close relative is an important consideration, especially if the diagnosis occurred at a young age.
Prior medical treatments, such as radiation therapy to the chest area, can elevate risk. Lifestyle factors like obesity after menopause and alcohol consumption are linked to an increased risk of breast cancer. Some lymphomas are also associated with a compromised immune system.