A lump found under the armpit (axilla) can be an alarming discovery, but most masses are not indicative of a serious condition. The armpit contains various tissues, including skin, fat, hair follicles, and a large cluster of lymph nodes, and a lump can originate from any of these structures. While some cases involve concerning diagnoses, the majority of axillary lumps are benign, temporary, and often related to routine immune responses or minor skin issues. Understanding the different origins and characteristics of these swellings helps determine when medical consultation is necessary.
Common Causes Related to Skin and Local Irritation
The most frequent causes of armpit lumps are benign conditions localized to the skin and underlying structures. These are typically temporary and result from irritation, blockage, or minor infection. Folliculitis, an inflammation of hair follicles, often occurs due to shaving or poor hygiene, presenting as small, tender, red bumps that resemble pimples.
Another common cause is a sebaceous cyst (epidermoid cyst), which is a closed sac under the skin filled with keratin. These cysts form when a hair follicle or oil gland duct becomes blocked. They tend to feel firm and are often painless unless they become infected or inflamed. A lipoma, a noncancerous growth of fatty tissue, feels distinctly different; it is soft, pliable, easily movable when pressed, and typically grows slowly without causing pain.
A chronic skin condition called Hidradenitis Suppurativa (HS) involves the clogging and inflammation of hair follicles and sweat glands, often appearing in the armpit and groin. HS causes painful, boil-like lumps that can persist, recur, or rupture. Irritation from antiperspirants, which contain aluminum-based compounds that block sweat ducts, can also lead to localized inflammation and swelling.
Swollen Glands: The Immune System’s Response
A significant portion of armpit lumps are swollen axillary lymph nodes, which are small, bean-shaped organs central to the body’s immune system. These nodes function as filters, trapping foreign particles, bacteria, and viruses from the lymph fluid draining from the arm, hand, and surrounding chest area. When the body detects an infection or illness, white blood cells inside the nodes multiply to fight the threat, causing the nodes to increase in size and become palpable.
This type of swelling, known as lymphadenopathy, is often tender or painful to the touch, and the node remains mobile under the skin. A simple infection in the hand or arm, a common cold, or a systemic illness like mononucleosis can trigger this immune response. The swelling typically decreases as the underlying infection or illness resolves.
Recent vaccinations, such as those for influenza or COVID-19, are another recognized cause of temporary axillary lymph node swelling, as the immune system actively mounts a response to the vaccine. This reaction most often occurs in the armpit on the same side where the injection was administered. While the swelling usually appears within a week of vaccination, it can sometimes take several weeks or even a few months before the node returns to its normal size.
Characteristics of Lumps Requiring Immediate Attention
While most lumps are benign, certain characteristics warrant prompt medical evaluation to rule out serious underlying conditions, such as cancer. A lump that is hard, fixed to the underlying tissue, and non-mobile is considered a “red flag” feature. Unlike an infected lymph node or a lipoma, a lump associated with malignancy often feels stony or irregular and cannot be easily moved under the skin.
Lumps that are painless are sometimes more concerning than those that are tender, as pain often indicates active infection or inflammation. Any axillary mass that persists for more than two to four weeks without shrinking should be evaluated, especially if it is growing rapidly. The presence of associated systemic symptoms alongside an armpit lump also increases the need for urgent consultation.
These warning signs include unexplained weight loss, drenching night sweats, or a persistent, low-grade fever, which are sometimes associated with lymphomas or other systemic cancers. In women, a lump in the armpit can sometimes be the first sign of breast cancer that has spread to the lymph nodes, underscoring the importance of examining the surrounding breast tissue for any changes. A medical professional should evaluate any lump with these features to ensure a timely and accurate diagnosis.
Steps in Medical Evaluation and Diagnosis
The evaluation of an armpit lump begins with a thorough medical history, focusing on the lump’s duration, recent illnesses or vaccinations, and whether it is painful or has changed in size. The physical examination involves careful palpation to assess its size, consistency (soft, firm, or hard), mobility (movable or fixed), and tenderness. The doctor will also examine the ipsilateral arm and breast tissue for any source of infection or other abnormalities.
If the physical examination is inconclusive or suggests a deeper mass, imaging studies are the next step. Axillary ultrasound is typically the initial imaging modality, as it can distinguish between a solid mass and a fluid-filled cyst, and allows for detailed visualization of the lymph nodes. For women over 30, diagnostic mammography is often performed alongside the ultrasound to evaluate the breast tissue for any underlying malignancy.
If the imaging results show suspicious features, such as a lymph node with a thickened outer layer (cortex) or a loss of its normal fatty center (hilum), a tissue sample may be necessary. This is typically done using an ultrasound-guided core needle biopsy or fine-needle aspiration, which safely extracts a small amount of tissue for laboratory analysis. The decision to pursue a biopsy is based on the combined findings of the history, physical exam, and imaging, with the goal of differentiating a benign process from a condition that requires specific treatment.