What Causes Lump Under Armpit?
The armpit is a busy area. It contains lymph nodes, sweat glands, hair follicles, and fatty tissue. When a lump forms, it usually comes from one of these structures reacting to something.
The most common causes fall into three groups: infections, skin conditions, and tissue growths. Infections cause lymph nodes to swell as they fight off germs. Skin conditions like ingrown hairs or blocked sweat glands create painful bumps. Tissue growths, which are usually benign, form when cells multiply abnormally.
Understanding which type you have helps you know whether to wait, treat it at home, or see a doctor.
Swollen Lymph Nodes: The Most Common Cause
Lymph nodes are small, bean-shaped glands that filter lymph fluid. They are part of your immune system. When your body fights an infection, these nodes fill with immune cells and enlarge.
In the armpit, lymph nodes drain fluid from the arm, chest wall, and upper back. This means an infection anywhere in those areas can cause an armpit lump. Common triggers include:
- Viral infections like a cold or flu
- Bacterial infections such as strep throat
- Skin infections on the arm or hand
- Recent vaccination on the same side
Swollen lymph nodes from infection are usually tender. They feel rubbery and move slightly when pushed. They often shrink within two to four weeks after the infection clears.
A hard, fixed, painless lymph node that grows steadily is different. That pattern warrants prompt medical attention because it can indicate lymphoma or metastatic cancer. Most swollen nodes are not cancer, but the distinction matters.
Hidradenitis Suppurativa: Blocked Sweat Glands
Hidradenitis suppurativa is a chronic skin condition that causes painful lumps under the arms, in the groin, and under the breasts. It occurs when hair follicles and apocrine sweat glands become blocked and inflamed.
These lumps look like deep, red pimples or boils. They can rupture and drain foul-smelling fluid. Over time, tunnels may form under the skin, connecting the lumps.
This condition is not an infection you can catch. It is an inflammatory disorder. Risk factors include smoking, obesity, and a family history of the condition. It affects women more often than men.
Treatment ranges from topical antibiotics and warm compresses for mild cases to biologic medications for severe disease. If you have recurring painful lumps in the armpit that come and go, hidradenitis suppurativa is a strong possibility.
Boils and Abscesses: Localized Infections
A boil, also called a furuncle, is an infection of a hair follicle. When the infection spreads deeper into the skin, it becomes an abscess. Both appear as red, swollen, painful lumps filled with pus.
Staphylococcus aureus bacteria cause most boils. The bacteria enter through a break in the skin, such as a cut, scratch, or ingrown hair from shaving.
A boil starts as a firm, red, tender lump. Over several days, it softens and develops a white or yellow center. The pain often increases as the pus builds up.
Small boils may drain on their own with warm compresses applied three to four times daily. Larger boils or those accompanied by fever require medical treatment. A doctor may need to incise and drain the abscess. Do not squeeze or poke a boil yourself. This can push the infection deeper.
Cysts: Benign Fluid-Filled Sacs
Epidermoid cysts and pilar cysts are common benign lumps that can appear in the armpit. These form when skin cells or hair follicle cells become trapped beneath the surface and produce keratin, a protein that fills the cyst.
Cysts feel like smooth, round bumps under the skin. They are usually painless unless they become inflamed or infected. They can grow slowly over months or years.
Many cysts do not require treatment. If a cyst becomes painful, red, or drains, see a doctor. Removal involves a minor procedure to excise the entire sac. If the sac is not fully removed, the cyst can recur.
Lipomas: Fatty Tissue Growths
A lipoma is a benign tumor made of fat cells. It feels soft, doughy, and movable under the skin. Lipomas are usually painless and grow very slowly.
These growths are common and almost never cancerous. They can occur anywhere fat tissue exists, including the armpit. Most lipomas do not require treatment unless they become large, uncomfortable, or press on nearby structures.
A doctor can usually diagnose a lipoma by feel alone. If there is any doubt, an ultrasound can confirm the diagnosis. Surgical removal is optional and done for cosmetic reasons or if the lipoma causes symptoms.
When a Lump Could Be Cancer
Cancer is the least common cause of an armpit lump, but it is the one people worry about most. The concern is valid, and the signs are specific.
Breast cancer can spread to lymph nodes under the armpit before it is felt in the breast itself. This is why clinical breast exams include checking the armpit. Lymphoma, a cancer of the lymphatic system, also commonly presents with swollen nodes in the neck, armpit, or groin.
Features that raise concern include:
- A lump that is hard and fixed to surrounding tissue
- A lump that does not move when pushed
- Steady growth over several weeks
- No associated pain or tenderness
- Lumps in multiple areas, such as both armpits or the neck
- Accompanying symptoms like unexplained fever, night sweats, or weight loss
None of these signs confirm cancer. Many benign conditions can mimic them. But these patterns warrant a medical evaluation rather than watchful waiting.
When to See a Doctor
Most armpit lumps resolve on their own or with simple home care. Some situations require professional evaluation.
See a doctor if the lump:
- Persists for more than two to four weeks without shrinking
- Grows progressively larger
- Is hard and does not move
- Is accompanied by redness, warmth, or fever suggesting infection
- Is accompanied by breast changes, such as a new breast lump or skin dimpling
- Returns in the same location after resolving
A doctor will examine the lump and ask about your medical history. Depending on findings, they may order an ultrasound, blood tests, or a biopsy. A biopsy is the only definitive way to determine if a lump is cancerous.
Do not wait indefinitely to have a persistent lump checked. Early evaluation is simple and provides peace of mind. If the lump is serious, early detection improves outcomes.
Home Care for Benign Lumps
For lumps you have confirmed are minor infections or skin irritations, home care can help. This applies to small, tender bumps consistent with swollen lymph nodes from a cold or small boils.
Warm compresses applied for 10 to 15 minutes several times daily can help small boils drain and ease lymph node discomfort. Over-the-counter pain relievers like acetaminophen or ibuprofen can manage pain.
Keep the area clean and dry. Avoid shaving over an active lump. Wear loose clothing to reduce friction. Do not attempt to pop, squeeze, or drain any lump yourself. This increases infection risk and can cause scarring.
If the lump does not improve within a week or worsens, stop home care and seek medical advice.
Frequently Asked Questions
Can deodorant cause a lump under the armpit?
Deodorants and antiperspirants can irritate the skin or block hair follicles, leading to ingrown hairs or small infected bumps. These are not true tumors, and switching products or pausing use often resolves the irritation.
How long does a swollen lymph node in the armpit last?
Lymph nodes swollen from a viral or bacterial infection typically shrink within two to four weeks after the infection clears. A node that stays enlarged longer than four weeks or keeps growing should be evaluated by a doctor.
Is a painful lump under the armpit more likely to be benign?
Painful lumps are more often caused by infections, inflamed cysts, or hidradenitis suppurativa, which are benign conditions. Painless, hard, fixed lumps raise more concern, though they can still be benign.
Should I get an armpit lump checked if it goes away and comes back?
Yes. Recurring lumps in the same location can indicate hidradenitis suppurativa, recurrent cysts, or chronic infection. A doctor can identify the underlying cause and recommend treatment to prevent repeat episodes.
