The armpit is a complex anatomical crossroads containing a dense network of structures that can all be sources of pain. This region is home to muscles, nerves, major blood vessels, and a significant cluster of lymph nodes. Because of this intricate arrangement, armpit pain is a common symptom that can stem from a simple muscle strain or minor skin irritation. However, it can also indicate a more serious underlying issue that requires medical evaluation.
Musculoskeletal and Nerve Issues
Pain originating from the muscles and nerves within the armpit is frequently linked to movement and physical activity. The armpit is bordered by several muscles, including the pectoralis major and the latissimus dorsi, which are prone to injury. A common cause of discomfort is a muscle strain in the chest or upper arm, often resulting from lifting weights or repetitive motions like throwing. This type of pain is usually localized and worsens when the affected muscle is stretched or contracted.
The pain may also result from nerve irritation, known as neuritis, as the brachial plexus—a major network of nerves supplying the arm and hand—passes directly through this area. Nerve pain can feel sharp, burning, or tingling. Conditions like Thoracic Outlet Syndrome can cause compression of these nerves and blood vessels as they exit the neck and pass into the armpit, leading to chronic pain, numbness, and weakness. Pain radiating into the armpit can also originate from the shoulder joint or the rotator cuff tendons.
Skin and Superficial Glandular Conditions
The skin of the armpit, with its natural warmth and moisture, is susceptible to superficial conditions that cause pain. Friction, shaving, and the use of deodorants or soaps can irritate the sensitive skin, leading to contact dermatitis or folliculitis. Folliculitis is an inflammation of the hair follicles, typically presenting as small, red, pimple-like bumps or pustules that are tender to the touch.
A more chronic and painful condition is Hidradenitis Suppurativa (HS), characterized by the blockage and inflammation of deep hair follicles and associated sweat glands. HS lesions appear as painful, deep nodules or boils that may rupture and drain, often recurring. HS can lead to the formation of sinus tracts—small tunnels under the skin—and significant scarring over time. Another painful cause is an ingrown hair, which can trap bacteria and result in a localized abscess or cyst.
Lymph Node Swelling and Immune Response
The axillary lymph nodes are a crucial component of the immune system, acting as filters that trap pathogens and abnormal cells draining from the arm, chest wall, and breast tissue. When the body detects an infection or inflammation, these nodes become activated, leading to lymphadenopathy, or swelling. This causes the lymph nodes to become enlarged, firm, and often painful or tender to the touch.
Most instances of painful, swollen lymph nodes are temporary and benign, caused by common infections like a cold, flu, or a localized skin infection. Recent vaccinations, such as the COVID-19 or flu shot administered in the arm, can also stimulate the immune response, causing temporary swelling and tenderness. Typically, nodes swollen due to infection or recent vaccination are mobile under the skin and resolve within a few weeks.
Serious Underlying Medical Concerns
While most armpit pain is benign, it can occasionally be a symptom of a more serious condition. Cancers, particularly breast cancer, often spread to the axillary lymph nodes, causing them to enlarge. While pain is rarely the sole symptom, new, persistent pain accompanied by a lump should be investigated. A lump that is non-mobile, hard, or rubbery, and does not decrease in size, raises concern for malignancy.
Cancers of the lymphatic system, such as lymphoma, can also cause persistent, unexplained swelling in the armpit nodes, sometimes accompanied by systemic symptoms. Furthermore, armpit pain can be referred pain originating from the chest. For example, angina or a heart attack can cause pain that radiates to the left arm, shoulder, and occasionally the left armpit. This referred pain is usually accompanied by other symptoms like chest pressure or shortness of breath.
When Medical Attention is Necessary
Knowing when to consult a healthcare professional is important for distinguishing between minor and serious causes of armpit pain. Medical evaluation should be sought if the pain is sudden and severe, or if it significantly limits daily arm movement. Persistent pain that lasts longer than one or two weeks without any obvious cause, like a recent strain or infection, also warrants a doctor’s visit.
Any lump found in the armpit should be evaluated if it is hard, fixed in place, rapidly growing, or if it does not become smaller over a few weeks. Additionally, pain accompanied by systemic symptoms are red flags that point toward a potentially serious underlying condition:
- Unexplained fever
- Night sweats
- Significant and unintentional weight loss
- Difficulty breathing