What Causes an Underarm Rash?

Whether itchy, inflammatory, bacterial, or fungal underarm rashes, these types of skin problems in your armpit can be mild or severe, short-lived or chronic. Treatments depend on the underlying cause; over-the-counter creams can work best for some rashes, while others require a prescription.

Whenever you have lingering symptoms—like an itchy, irritated armpit—see a healthcare provider, such as a dermatologist specializing in skin conditions. Keep reading to learn more about armpit rashes and what to do about them.

1. Contact Dermatitis

This rash is caused by exposure to something that irritates the skin or causes an allergic reaction. There are two main types of contact dermatitis, and each can cause an itchy, burning, or painful rash:

• Allergic contact dermatitis occurs when the skin comes in contact with a substance that provokes an immune response. Your rash could be an allergic reaction to fragrances, preservatives in soap and skin products, or poison ivy (presuming you recently had a brush with this poisonous plant).
• Irritant contact dermatitis is the more common type of contact dermatitis. It's caused by repeated exposure to an irritant. Such exposures may include applied products such as deodorants, antiperspirants, soaps, or washes.

Some ways to treat symptoms are to avoid the allergen or irritant and wash away any irritants on the skin. In some cases, creams and medications may be necessary to treat contact dermatitis.

2. Hidradenitis Suppurativa (HS)

Also known as acne inversa, HS is a chronic inflammatory skin condition. It begins as a blockage of hair follicles in areas of the body where certain sweat glands (called apocrine sweat glands) reside. In its mildest form, HS produces small, painful, pus-filled bumps. They may look reddish, purplish, or darker brown, depending on a person's skin color.

As HS progresses, larger nodules can develop. The bumps can rupture and leak foul-smelling fluid and pus. Tracks or tunnels connecting the wounds may form beneath the surface of the skin, leading to scarring and even keloids.

Various surgical procedures may be helpful in general, but treatment often depends on the severity of the disease, which is as follows:

• Mild: Topically applied cleansers and antibiotics
• Moderate: Various oral medications and combination therapies
• Moderate-to-severe: Adalimumab (Humira), an injectable biologic

3. Folliculitis

A zit-like rash in your armpits could be folliculitis. Folliculitis is a common condition that occurs when hair follicles become infected. You might develop it because of shaving and waxing, wearing tight clothing, or taking certain medications.

Treatment may depend on the type and severity of the rash. For a mild, pimply rash, it may be best to stop shaving for a couple of days and apply an over-the-counter topical steroid, like hydrocortisone cream. For a more severe rash, where the bumps are topped by pustules, or little whiteheads, you may need an antibiotic.

4. Acanthosis Nigricans (AN)

AN is not a rash but instead a velvety thickening of the skin in the body's folds and creases, including the armpits. These patches appear darker in color than the surrounding skin.

People who are overweight, have a family history of AN, or have darker skin are at greater risk of developing this skin condition. In addition, acanthosis nigricans has been linked to:

• Hormonal irregularities like thyroid disease
• Insulin resistance due to diabetes or pre-diabetes, for example
• The use of certain drugs, such as birth control pills or steroids

Addressing an underlying medical cause may be part of AN treatment. To reduce the appearance of AN, healthcare providers may suggest oral or topical retinoids to help clear the skin, laser treatments to reduce the skin thickness, or topical medication to lighten the skin.

5. Intertrigo

Chafing, or skin rubbing against skin—especially in warm or moist areas of the body—can cause intertrigo. It's an itching, burning rash that can appear red or reddish-brown but only affects the outer layers of skin.

These so-called intertriginous areas can ooze, crack, or bleed, and as the skin breaks down, it becomes vulnerable to infection. In addition, you may develop a yeast, bacterial, or fungal underarm rash with intertrigo.

Keeping skin folds cool and dry can help with healing and prevent recurrences. Treatment options include antibiotic or antifungal creams, topical steroid cream, and drying agents (such as antiperspirant or absorbent powder).

6. Inverse Psoriasis

Also called intertriginous psoriasis, this is a type of rash that affects the body's skin folds. Unlike the white, scaly patches that psoriasis usually produces, inverse psoriasis can be smooth and shiny. The rash can be sore, itchy, and irritated from sweating.

Topical steroids are usually the first choice of treatment. More severe cases, however, may require oral medication or biologic therapy.

7. Ringworm

Ringworm is an itchy, scaly rash that forms a ring-like pattern on the skin. It belongs to a group of diseases called tinea, caused by fungi. It spreads via contact with an infected person or animal or by touching a surface where the fungi like to live.

You can also get ringworm by sharing towels or other personal items with someone who has the infection. Ringworm is typically treated topically with an over-the-counter or prescription antifungal medication.

8. Cutaneous Candidiasis (Yeast)

Yeast thrives in warm, moist creases of the body, like your armpits, and candidiasis is simply a yeast infection of the skin. The same fungus that causes most vaginal yeast infections, Candida albicans, is often responsible for skin infections too. These infections result from an overgrowth of yeast normally found on your skin.

You may have discolored rash on your skin folds or hair follicle infections. Treatments might include using drying powders, keeping your skin dry, or applying antifungal products like creams or ointments.

9. Heat Rash (Prickly Heat)

You can get a pimply underarm rash from being overheated. This type of rash (also called miliaria) occurs when sweat glands and ducts become obstructed by bacteria, skin cells, oil, or other debris.

Clusters of pimples or small blisters can make your skin feel itchy or irritated—causing prickly, tingling pain. A heat rash should still clear up on its own if you keep your skin cool and dry. In some cases, a healthcare provider may recommend a prescription lotion to reduce discomfort.

10. Cutaneous Lymphoma (Skin Lymphoma)

Cutaneous lymphoma, or lymphoma of the skin, is an uncommon type of cancer. It begins in white blood cells called lymphocytes, which are part of the body's immune system.

Skin lymphomas may appear as pimples, flat patches, thick plaques, or nodules. They may be itchy and range in color from red to purple. If cancer reaches the lymph nodes, you may feel a lump in your armpit area.

Most skin lymphomas have no known cause. A weakened immune system can boost your risk of developing skin lymphoma, although it's unclear why. Various treatments may be recommended depending on the type, location, and stage of cancer.

A Quick Review

There are various causes of armpit rashes. You might have a fungal underarm rash due to ringworm or yeast infections or an itchy armpit rash because of intertrigo or heat rash.

See a healthcare provider, such as a dermatologist, to help determine the reason for your underarm rash to receive the proper treatment. Depending on the cause, treatments will vary from creams and ointments to cleansers, powders, or surgical options.