Finding a lump in your armpit can be concerning, especially if you don’t know what’s causing it. Anyone can develop underarm lumps, which usually aren’t a cause for concern.

One type of armpit lump is a cyst, which can be seen in hidradenitis suppurativa (HS) and a variety of other skin conditions. One member of myHSteam said, “Tomorrow I have an appointment with a plastic surgeon to evaluate my armpit lump.”

What Could Cause an Armpit Lump?

Most of the time, an armpit lump occurs due to a disruption in the hair follicles, sweat glands, lymph nodes, muscle, or skin. There’s a lot going on in the underarm region, and an infection or injury to one of those structures can cause a lump or cyst. Common examples of these disruptive conditions include:

• Inflamed hair follicles
• Boils or carbuncles
• Cysts around hair follicles
• Folliculitis (infection of the hair follicle)
• Ingrown hairs
• Lipomas (balls of fat cells)
• Shaving irritation
• Swollen lymph nodes from viral infections or vaccinations

Rare cases of underarm lumps include both benign (noncancerous) and cancerous tumors, including breast cancer and lymphoma.

This article focuses on possible causes of a cyst in the armpit. Cysts are pockets of fluid that vary in size but are usually inflamed, painful, and close to the skin’s surface. Remember, as with any new symptom, reach out to a medical professional for an evaluation and appropriate treatment if you develop an armpit cyst.

Blocked Sweat Glands

As you likely know if you’ve ever experienced a hot summer’s day or a stressful meeting at work, the underarm is filled with sweat glands. A sweat gland can become blocked for many reasons, including the use of certain deodorants or antiperspirants, infrequent bathing, or excessive sweating. An infected sweat gland may cause a painful or tender cyst because the infected material can’t make its way out of your pores. The affected area may be discolored, tender, and irritated.

If you suspect you have a blocked sweat gland, take these steps to help avoid discomfort:

• Keep the area clean and as dry as possible.
• Wear loose-fitting clothing.
• Ask your doctor if you should use over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs) to reduce inflammation and pain.

Infected Hair Follicle

The armpit also contains a high density of hair follicles. Hair follicles are prone to bacterial infections, most commonly a staph infection, which can cause small cysts to form. These bumps may be painful or itchy. You may notice them after shaving your underarms or using a hot tub.

Infected hair follicles can range in size. A very small area affected by folliculitis can grow into a boil. Boils that spread into the surrounding skin and cluster together form what is called a carbuncle. A carbuncle may be itchy and sensitive, with a yellow or white “head.”

Prevent infected hair follicles by washing up regularly, using a clean towel to dry yourself, and avoiding shaving if you can. If you’re currently experiencing folliculitis, use a warm compress to relieve inflammation, and try over-the-counter antibacterial cream to resolve a mild case. If your infection grows, persists, or reappears, it may be a good idea to be seen by a dermatologist to drain the fluid from your lesion.

Hidradenitis Suppurativa

HS is a chronic skin condition characterized by inflamed hair follicles, which often occur in areas where the skin rubs together, including the armpits and groin. “There is always at least one lesion present in both of my armpits,” one myHSteam member said.

If you’ve experienced recurrent painful lumps, abscesses, and scarring in your underarms and other skin folds, talk to your health care provider about HS.

HS is thought to be caused by a variety of factors, such as genetics and hormones. It isn’t caused by bad hygiene, and it’s not contagious to others. The groups most likely to get HS are women, African Americans, people who smoke, and individuals with higher body weights, according to Johns Hopkins Medicine. However, many people who don’t have these associated factors also get HS.

Treating HS in the long term may require a combination of lifestyle changes recommended by your doctor, such as quitting smoking. Medications to treat an HS flare include antibiotics, corticosteroids, and biologics. Sometimes, in severe cases with repeated HS flares, surgery like incision and drainage may be an option. In other instances, the surgeon may remove the sweat glands entirely.

One myHSteam member said, “My surgeon took out my sweat glands from under my arms, and I no longer get HS cysts.”

Treating Armpit Cysts

If you notice a single cyst in your armpit, watchful waiting may be the best approach. Avoid picking at or further disrupting your underarm. Use warm compresses, take NSAIDs, and apply topical antibacterial cream while keeping the area warm and dry. Wrap the area with a sterile bandage to reduce friction and irritation, if possible. For the next few days, watch the cyst over time to see if it gets better or worse.

Contact a doctor if any of the following situations occur:

• The cyst persists for more than a few days — You may need prescription medicine from a dermatologist. “I now have a script for doxycycline to use when I get a flare,” one myHSteam member said.
• You have a fever or other signs of illness — The infection may have spread and requires medical care. “My underarm cyst popped, but since then, I’ve had a fever, chills, migraine, and vomiting,” one member said. These are signs that you should see a doctor right away.
• This is not your first cyst — You may have a chronic skin disease such as HS, which requires long-term treatment and prevention.

When in doubt, speak to your doctor for medical advice regarding what may have caused your armpit cyst, what treatment options are available to you, and how to prevent skin infections in the future.

Talk With Others Who Understand

On myHSteam, the social network for people with hidradenitis suppurativa and their loved ones, more than 39,000 members come together to ask questions, give advice, and share their stories with others who understand life with HS.

Have you experienced an armpit cyst? What advice do you have for others who notice a lump in their underarm? Share your experience in the comments below, or start a conversation by posting on your Activities page.