Pea-Sized Lump in Armpit That Hurts: Causes and Care

What Can a Painful Pea-Sized Armpit Lump Mean?

The armpit contains lymph nodes, hair follicles, sweat glands, breast tissue, fat and blood vessels. A lump can develop in any of these structures.

A pea-sized lump may be visible on the skin or noticeable only when you touch the area. It might feel soft, firm, smooth or slightly movable.

Size alone cannot identify the cause. Healthcare professionals also consider:

• Whether the lump is close to the skin or deeper in the armpit
• Whether it is red, warm or draining pus
• Whether it moves beneath the skin
• How quickly it appeared
• Whether it is growing or shrinking
• Whether similar lumps have occurred before
• Whether there are symptoms elsewhere in the body

The following patterns may offer clues, but they cannot confirm a diagnosis.

Common Causes of a Painful Armpit Lump

Reactive Lymph Node

Lymph nodes are small structures that help the immune system respond to infections and other threats. The armpit contains a group of lymph nodes that receive fluid from the arm, breast and chest wall.

An armpit lymph node may become swollen after:

• A vaccination in the same arm
• A cut, insect bite or infection on the arm
• A breast infection
• Infection or inflammation near the chest or armpit
• Certain broader infections or immune conditions

A reactive lymph node may feel tender and slightly movable. It may appear suddenly and gradually become smaller as the underlying problem improves.

Tenderness can support an inflammatory explanation, but it is not a reliable way to rule out a serious condition. According to the American Academy of Family Physicians, healthcare professionals assess lymph nodes based on their location, duration, consistency and associated symptoms rather than relying on one feature.

Ingrown Hair or Inflamed Hair Follicle

A small, painful bump near the skin surface may come from a hair follicle rather than a lymph node.

An ingrown hair develops when a hair grows back into the skin. Shaving, waxing, friction and tight clothing can increase the likelihood of irritation.

When the follicle becomes inflamed, it is called folliculitis. It may cause red, tender or pus-filled bumps around individual hairs.

Possible signs include:

• A red or irritated bump
• A visible trapped hair
• A white or pus-filled center
• Tenderness when touched
• Pain during shaving or arm movement

Avoid shaving over the area until it heals. Do not squeeze or pick at the bump because this may push bacteria deeper into the skin.

Seek medical care if redness spreads, pain increases, several bumps appear or you develop a fever.

Boil or Skin Abscess

A boil or abscess is a pocket of infection that contains pus. It can begin as a small, firm and painful lump before becoming larger, softer or more swollen.

A skin abscess may:

• Feel warm and painful
• Look red or darker than the surrounding skin
• Develop a soft center
• Leak pus
• Cause fever or a general feeling of illness

Skin redness may be less noticeable on brown or black skin. Warmth, swelling and tenderness may be easier to recognize.

Some small boils drain without medical treatment. However, an abscess may need to be drained by a healthcare professional. Do not puncture or squeeze it yourself.

Seek prompt medical care if the lump grows quickly, pain becomes severe, redness spreads or fever develops. People who experience recurring boils should also discuss the pattern with a healthcare professional, especially if the lumps appear in the same areas.

Skin Cyst

A skin cyst is a sac that develops beneath the skin and may contain fluid, skin cells or thicker material.

A cyst often:

• Feels round and smooth
• Sits close to the skin
• Grows slowly
• Moves slightly when pressed
• Becomes painful when inflamed or infected

Unlike a reactive lymph node, a cyst may remain after the pain and inflammation improve. Some cysts also have a tiny opening or dark spot on the skin.

A small, painless cyst may not require treatment. Medical care may be necessary if it becomes infected, repeatedly inflamed or continues to grow.

Hidradenitis Suppurativa

Hidradenitis suppurativa is a long-term inflammatory skin condition. It causes deep, painful lumps in areas where skin touches skin, particularly the armpits and groin.

According to the American Academy of Dermatology, the first sign may look like a pimple or boil.

Other signs include:

• Lumps that return in the same place
• More than one lump
• Drainage or an unpleasant smell
• Small tunnels beneath the skin
• Scarring after a lump heals
• Similar lumps beneath the breasts, in the groin or around the buttocks

Hidradenitis suppurativa is not caused by poor hygiene. Early assessment by a dermatologist may help reduce inflammation, scarring and repeated flare-ups.

Lipoma

A lipoma is a noncancerous growth made of fat cells. It usually feels soft, moves under the skin and grows slowly.

Lipomas are generally painless. However, one may cause discomfort if it presses on nearby tissue or develops in an area exposed to repeated friction.

Because a lipoma is usually not tender, a new painful pea-sized lump is more likely to have another explanation. A healthcare professional may still consider a lipoma if the lump has been present for a long time.

Although both can cause lumps beneath the skin, lipomas and lymphoma have different features. They still cannot be reliably distinguished by touch alone.

Why Does the Lump Hurt When Touched?

Pain usually means that nearby tissue is irritated or inflamed. Pressing the lump may place pressure on sensitive tissue and nerve endings.

A lump may hurt when touched because of:

• Inflammation in a lymph node
• Irritation from shaving
• An infected hair follicle
• Pressure from fluid or pus
• Friction from clothing
• Repeatedly checking or pressing the area

Avoid examining the lump several times a day. Frequent pressing can increase tenderness and make the area seem more painful even if the lump is not growing.

Check it every few days instead. Note whether its size, pain, skin colour or warmth is changing.

What If the Lump Is Under the Skin but Not Visible?

A lump can be felt without being visible. Lymph nodes, lipomas and some cysts develop beneath the skin, so they may not change the skin’s appearance.

A deeper lump may be noticed while showering, shaving or applying deodorant. Once discovered, it is easy to check it repeatedly and become more aware of the area.

Do not assume that an invisible lump is either harmless or dangerous. Its depth and appearance cannot identify the cause.

Arrange a medical appointment if a deep lump grows, becomes fixed, remains painful or does not begin improving within about two weeks.

What Can You Do at Home?

Home care depends on where the lump is located and what other symptoms are present.

For a Skin-Level Bump

If the bump appeared after shaving and looks like an irritated follicle:

• Stop shaving temporarily.
• Keep the area clean and dry.
• Wear loose clothing.
• Avoid scented deodorants if they cause irritation.
• Do not squeeze or puncture the bump.

A warm, clean compress may ease discomfort from a small boil or inflamed follicle. Stop home care and seek advice if the lump worsens.

For a Possible Reactive Lymph Node

A tender node associated with a recent vaccination or nearby infection may gradually shrink as the underlying problem improves.

Avoid repeatedly pressing it. Record when it appeared and whether it is changing.

Do not assume that a persistent lump is still related to a past illness or vaccination. Arrange an examination if it does not improve.

For a Deep or Unexplained Lump

Do not try to drain, massage or treat a deep lump at home.

Arrange a medical appointment if you cannot identify a clear skin-related cause, particularly if the lump is new, growing or only on one side.

When Should You Seek Medical Care?

Seek Prompt or Same-Day Care If:

• The lump grows rapidly.
• The area becomes very painful, hot or swollen.
• Pus is draining from the lump.
• Redness or swelling is spreading.
• You have a fever or feel significantly unwell.
• Swelling affects the movement of your arm.
• You are breastfeeding and develop breast redness, worsening pain or flu-like symptoms.

Arrange a Medical Appointment If:

• The lump does not begin improving within about two weeks.
• It feels hard, irregular or fixed.
• It repeatedly returns.
• It continues to grow.
• You have swollen lymph nodes in other areas.
• You notice a breast lump or nipple change.
• You have unexplained weight loss, night sweats or persistent fever.
• You have a history of cancer.

Breast redness, swelling, skin thickening or other early breast skin changes should be medically evaluated, particularly when they develop quickly or affect only one breast.

How Doctors Check an Armpit Lump

A healthcare professional will first ask when the lump appeared, whether it has changed and if you recently had a vaccination, skin infection, injury or breast symptoms.

During the examination, they may check:

• The lump’s size and location
• Whether it feels soft, firm or fluid-filled
• Whether it moves beneath the skin
• Whether the area is warm, red or tender
• Other lymph nodes in the neck or groin
• The nearby arm, chest and breast when relevant

An ultrasound may be recommended when the cause is unclear. It can help show whether the lump is a lymph node, cyst, abscess or solid mass. The American College of Radiology considers axillary ultrasound an appropriate initial imaging test for a new, one-sided armpit lump in women.

Breast imaging may also be needed when the person has breast or nipple changes or other concerning findings.

Most small armpit lumps do not require a biopsy. However, a tissue sample may be recommended if the lump continues to grow, remains unexplained or has concerning features on imaging.