Armpit Pain: Common Causes and When to Worry

What is in the armpit

The armpit is a crowded space. Its contents explain the range of causes:

• Lymph nodes (about 20 to 40), which drain the arm, chest wall and breast
• Sweat and oil glands and hair follicles
• Muscles at the edges: the pectoral muscles in front and latissimus dorsi behind
• The brachial plexus, the bundle of nerves supplying the arm
• The axillary artery and vein
• Breast tissue, which extends toward the armpit as the "axillary tail"

Common causes of armpit pain

Muscle strain

Pushups, bench press, throwing, swimming, lifting a child or moving furniture can strain the pectoral muscles or the muscles at the back of the armpit. Pain worsens with arm movement and pressing on the muscle, and there is no lump. See muscle strain.

Skin irritation, ingrown hairs and boils

• Razor burn and ingrown hairs: small, tender red bumps after shaving.
• Contact dermatitis: an itchy or stinging rash from deodorants, antiperspirants or laundry products.
• Folliculitis and boils: an infected hair follicle becomes a painful, pus-filled lump.

Swollen lymph nodes

Nodes swell when they fight an infection in the arm, hand, breast or chest wall, or after a cold or a vaccine (COVID-19, flu and others) in that arm. They feel like soft, tender, movable beans and shrink within a few weeks. See swollen lymph nodes. An infected node itself, lymphadenitis, is red, hot and very painful.

Hidradenitis suppurativa

Hidradenitis suppurativa is a long-term inflammatory condition of hair follicles in skin folds. It causes repeated painful lumps and abscesses in the armpits, groin and under the breasts, which drain and leave tunnels and scars. It often starts after puberty and is more common in women, smokers and people with excess weight.

Less common causes

• Shingles: burning or stabbing pain in a band on one side, followed a few days later by a blistering rash. See shingles.
• Breast conditions: breast pain often extends into the armpit, especially before periods. Mastitis in breastfeeding causes a red, painful breast and sometimes armpit tenderness. Breast cancer can spread to armpit nodes, usually causing a hard, painless lump.
• Lymphoma and other cancers: firm, painless, enlarging nodes, sometimes with sweats and weight loss.
• Nerve compression: a pinched nerve in the neck or thoracic outlet syndrome causes pain, tingling and weakness running into the arm.
• Blood clot in the axillary vein: sudden arm swelling, heaviness and bluish discoloration, more common in athletes with repetitive overhead movement or with catheters in the arm.
• Heart pain (angina or heart attack): pain in the left armpit or arm, usually with chest pressure, breathlessness or sweating.
• Cat-scratch disease: a tender armpit node 1 to 3 weeks after a cat scratch on the arm.

Armpit pain in women

Hormonal breast pain (cyclical mastalgia) can spread to the armpit in the week before a period. Breast tissue in the armpit can swell in pregnancy and while breastfeeding, sometimes forming a tender lump. Women are also more likely to have hidradenitis suppurativa. Any persistent armpit lump in a woman should be assessed along with a breast exam and, depending on age, imaging.

Left vs right armpit pain

Most causes affect either side equally. On the left, consider the heart if pain comes with exertion, chest discomfort or breathlessness. On either side, think about the arm or breast on that side as the source of a swollen node.

How doctors find the cause

Your doctor will ask how long you have had pain, whether there is a lump, recent exercise, shaving or new products, infections, vaccines, and breast symptoms. They will examine the armpit, skin, arm, breast and other lymph node areas. Tests may include:

• Ultrasound of a lump, which distinguishes nodes, cysts, abscesses and fat lumps
• Mammogram in women over about 30 with a lump
• Blood tests for infection or inflammation
• Swab of pus to guide antibiotics
• Biopsy of a persistent or suspicious node

Treatment and home care

• Muscle strain: rest from the triggering activity, ice in the first 48 hours then heat, gentle stretching, and ibuprofen or acetaminophen (paracetamol) following the label dose.
• Skin irritation: stop the new product, let shaving rash heal, and use a fragrance-free deodorant. Shave in the direction of hair growth with a clean blade.
• Small boils: warm compresses 3 to 4 times a day. Do not squeeze. See a doctor if one is large, very painful, or you have fever.
• Swollen nodes: treat the underlying infection and watch for shrinking over 2 to 4 weeks.
• Hidradenitis suppurativa: antiseptic washes, antibiotics, biologic medicines and sometimes surgery, guided by a dermatologist. Stopping smoking and losing weight help.
• Shingles: antiviral medicine works best started within 3 days of the rash.

Frequently asked questions

What causes armpit pain without a lump?

Common causes are a strained chest or shoulder muscle, skin irritation from shaving or deodorant, early shingles before the rash appears, a pinched nerve, and breast pain spreading into the armpit. Left armpit pain with chest discomfort or breathlessness needs urgent assessment for heart causes.

Is a painful lump in the armpit serious?

Usually not. Painful lumps are most often swollen lymph nodes from an infection, boils or infected hair follicles, which settle with time or treatment. Hard, painless lumps that grow or last more than 2 to 3 weeks are more concerning and should be examined.

Can deodorant cause armpit pain?

Yes. Fragrances and other ingredients in deodorants and antiperspirants can cause irritant or allergic contact dermatitis, with stinging, itching and redness. Applying to freshly shaved skin makes it worse. Switching to a fragrance-free product usually solves it.

Can armpit pain be related to the heart?

Occasionally. Angina or a heart attack can cause pain in the left armpit or arm, usually with chest pressure, shortness of breath, sweating or nausea, often triggered by exertion. Call 911 or your local emergency number if you have these symptoms.

How long do swollen armpit lymph nodes last after a vaccine?

They usually shrink within a few weeks, though they can last up to about 4 to 6 weeks. If a node is still enlarged after that, or keeps growing, have it checked.