6 causes of underarm rashes and how to avoid irritating your armpits

• An armpit rash is often caused by irritation from sweat, friction, soap, or dryness.
• It could also be an allergic reaction to fragrances or propylene glycol (a deodorant ingredient).

Rashes are pesky patches of irritated skin that can affect any part of your body, including your armpits.

Typically, armpit rashes aren't dangerous, but they can certainly be uncomfortable and range from itchy to painful. If you're experiencing a persistent rash alongside other symptoms, it's best to see a doctor to figure out what's going on.

Here are six potential causes of armpit rashes and how to treat them.

1. Contact dermatitis

Armpit rashes can be due to either irritant contact dermatitis or allergic contact dermatitis.

Irritant contact dermatitis of the armpit results in a red, inflamed rash, caused by an external substance, says Dr. Christopher G. Bunick, a dermatologist at Yale Medicine and an associate professor of dermatology at Yale School of Medicine.

This occurs when some kind of substance irritates your skin, damaging its outermost layer. It is due to irritation, not an allergy.

Bunick says common causes of irritant contact dermatitis in the armpits include:

• Sweat
• Friction due to movement or clothing
• Skin dryness
• Low humidity
• Soaps
• Excessive washing

Allergic contact dermatitis also results in a red, inflamed rash. However, this rash occurs due to an allergy to something that's coming into contact with your skin, says Dr. Hyemin Pomerantz, a board-certified dermatologist at VivaSkin Dermatology and Aesthetics.

"Your skin can become allergic to a certain ingredient of a product. An allergic reaction can happen at any time –– even to the product you've been using for a long time," Pomerantz says.

Common offenders are fragrances in perfume or cologne or propylene glycol which is in some deodorants, says Pomerantz.

Other symptoms of irritant contact dermatitis include:

• Hyperpigmented patches of skin that may be leathery (most common in people of color)
• Scaly, cracked, and dry skin (most common in white people)
• Blisters that may ooze and crust over
• Burning

How to treat it: The key to treating this is to determine what is causing the irritation or allergy and then eliminate it, Bunick says.

Additionally, you can apply a topical steroid for a couple of weeks to soothe irritation and inflammation, he says. In more serious cases, your doctor might prescribe you non-steroidal anti-inflammatory topicals.

2. Folliculitis

Folliculitis occurs when your hair follicles are inflamed, typically due to bacteria. Since there are plenty of hair follicles in your armpits, it's a common place for the condition to occur. Bunick says the most frequent cause is a staphylococcus (staph) infection. Folliculitis will result in red papules, bumps, or even larger boils that can be painful. The rash can also be itchy.

How to treat it: Topical antibiotics are usually the first course of treatment. In more serious cases, Bunick says you might need to take oral antibiotics to clear up the bacterial infection.

It's also important to take measures to prevent it from happening again. Bunick says preventative measures include shaving with clean razors (if you shave your armpits) and using benzoyl peroxide washes to lessen the chances of bacteria infecting your underarm hair follicles.

3. Yeast infection

A yeast infection is a type of fungal infection. "Yeast and fungus are very common in our environment. They love to grow in moist and warm environments, so it's not surprising that they may overgrow on our armpits," Pomerantz says.

This overgrowth of yeast can cause inflammation and a rash. Symptoms of a yeast infection on the skin of your armpit include:

• Bright red rash
• Itching
• Burning
• Spots that look like pimples

How to treat it: Your doctor may prescribe antifungal treatment, either topical or oral, depending on the individual case, says Pomerantz.

You can also make some minor changes to reduce your risk of recurring infections, including:

• Avoiding tight clothing
• Maintaining good hygiene
• Changing your bra frequently
• Treating any other underlying skin conditions

4. Seborrheic dermatitis

"Seborrheic dermatitis is an inflammatory skin rash that can be confused with eczema or psoriasis," Bunick says. While this condition is most common on the scalp, it can also show up in the armpits.

Symptoms of a seborrheic dermatitis rash include:

• Greasy skin patches covered in scales
• Hyperpigmentation or hypopigmentation in people of color
• Redness in white people
• Itching

How to treat it: Since fungus may cause seborrheic dermatitis, the rash often responds to antifungal medications, says Bunick. Usually, it will be a topical antifungal but more serious cases may need oral antifungal medications. Topical steroids can help with inflammation, too.

5. Psoriasis

Psoriasis is a condition related to the immune system. There is a specific type of psoriasis known as inverse psoriasis which primarily affects regions where there are skin folds –– including the armpits. There are typically less thick scales present in inverse psoriasis than in traditional psoriasis, Pomerantz says.

Some symptoms of the rash associated with inverse psoriasis are:

• Rash that may range in color, from pink to red or purple to brown
• Cracks in the skin
• Patches of skin might feel moist to the touch
• Itching

How to treat it: There's no cure for inverse psoriasis, but your doctor can prescribe various treatments to help relieve your symptoms. Pomerantz says some options include topical medications, oral medications, injections, and light treatments.

6. Acanthosis nigricans

Acanthosis nigricans is a condition often linked to obesity and/or diabetes, and it presents as skin darkening, brown to dark brown in color, with a "velvety thickening," Bunick says. People who see this in their armpits may also have it in other body creases.

Other symptoms include:

• Itchiness
• Odor in the area
• Skin tags

How to treat it: Bunick says using a topical retinoid can help reduce pigmentation and thickening of the affected areas. To control any pain or odor, your doctor might also prescribe other medications or creams.

Additionally, Bunick says it's important to address the underlying causes by losing weight or controlling your blood sugar, as directed by your doctor.

Insider's takeaway

Irritants, allergies, bacteria, fungus, and more can result in armpit rashes that vary in severity.
If there is any kind of troublesome rash in your armpits and you're experiencing discomfort, especially if the rash is persistent, it's best to see your doctor. They can help determine the exact type of rash and prescribe any necessary treatments to get you feeling better.