The region beneath the shoulder, known medically as the axilla, is a complex anatomical space containing skin, sweat glands, muscle tissue, nerves, blood vessels, and lymph nodes. Soreness or discomfort felt in the armpit can stem from many different origins due to this density of varied structures. The pain can range from superficial burning or itching to deep, aching discomfort. Understanding the location and nature of the pain is the first step in determining whether the cause is a simple surface issue or something more systemic.
Common Surface Irritations and Infections
The thin, sensitive skin of the armpit is frequently exposed to friction, moisture, and chemical irritants, which often leads to the most common types of soreness. Contact dermatitis is a frequent culprit, occurring as an allergic or irritant reaction to ingredients found in deodorants, antiperspirants, soaps, or even laundry detergents. This typically presents as a red, itchy, or burning rash confined to the area that came into contact with the product.
Another source of superficial pain is folliculitis, which is the inflammation or infection of hair follicles, often caused by shaving. After hair removal, the remaining stubble can curl back into the skin, leading to ingrown hairs that develop into small, tender, pus-filled bumps. Similarly, intertrigo is a rash that develops when skin folds rub against each other, trapping heat and moisture, creating a perfect environment for bacterial or fungal growth, leading to raw, red skin that may sting, itch, or burn.
More painful skin conditions can involve the blockage of hair follicles and associated sweat glands, leading to abscesses. Hidradenitis suppurativa (HS), for instance, is a chronic inflammatory condition that causes recurring, deep, painful lumps and boils to form in the armpit and other skin-fold areas. These lesions can persist for weeks, sometimes rupture, and often result in scarring and narrow channels, called sinus tracts, under the skin. Localized infections, such as a simple boil or carbuncle, can also cause acute, throbbing pain and swelling.
Swelling and Pain Related to Lymph Nodes
A deep, tender, or lumpy feeling in the armpit often originates from the axillary lymph nodes, which are small, bean-shaped structures that serve as filters for the body’s immune system. These nodes contain specialized white blood cells that trap pathogens and abnormal cells from the lymphatic fluid draining the arm, upper chest, and breast tissue. When the body detects an infection or illness, the nodes activate and swell, a condition known as lymphadenopathy, which causes localized pain and tenderness.
The most frequent cause of swollen axillary lymph nodes is a systemic infection, such as a cold, the flu, or a localized infection like cellulitis on the hand or arm. In these cases, the nodes are usually soft and moveable, swelling in response to the body fighting the illness elsewhere. The swelling is typically temporary, subsiding once the underlying illness resolves, though the nodes may remain slightly enlarged for a couple of weeks.
However, lymphadenopathy can also be a reaction to less common issues, including certain autoimmune disorders or, less frequently, the spread of cancer cells from nearby tissues like the breast. Unlike the soft, tender nodes caused by infection, nodes that signal a more serious underlying condition may feel hard or fixed in place. Because the armpit is the primary drainage route for the breast, any persistent or unexplained swelling in this area warrants careful medical evaluation.
Pain Originating from Muscle Strain
Soreness that feels deep, dull, and aching, especially when exacerbated by movement, is frequently musculoskeletal in origin. The armpit is a junction point for several powerful muscles involved in shoulder and arm movement, including the pectoralis major and minor and the latissimus dorsi. These muscles can suffer a strain from overuse or unaccustomed physical activity.
Activities like heavy weightlifting, particularly bench presses or pull-ups, or repetitive motions in sports can overstretch or tear the muscle tissue, with the pain radiating into the armpit area. A latissimus dorsi strain, for example, can cause a sharp pain near the back fold of the armpit during overhead pulling movements. The pain is typically reproducible when the injured muscle is contracted or stretched, which helps distinguish it from skin or lymph node issues.
Referred pain from the shoulder joint or the upper back can also be felt in the axilla. Issues like bursitis or a rotator cuff injury may present with discomfort that travels down the arm and seems to settle under the armpit. This type of muscular pain often responds well to rest, ice application, and over-the-counter anti-inflammatory medications.
Indicators That Require Professional Medical Advice
While most causes of armpit soreness are minor and resolve on their own, certain indicators suggest the need for professional medical attention. You should consult a healthcare provider if the soreness is accompanied by any of the following:
- Sudden, severe, or debilitating pain that limits arm movement.
- A lump that feels hard, is fixed in place, or is painless, as these characteristics are less typical of benign causes.
- A swollen lymph node that persists for longer than two weeks or continues to increase in size.
- Systemic symptoms, including unexplained fever, night sweats, or unintentional weight loss.
- Signs of a rapidly spreading infection, such as red streaks extending away from the armpit, increasing warmth, or significant surrounding swelling, which may indicate cellulitis requiring immediate antibiotic treatment.