How to treat an underarm rash

What could be causing the rash?

Intertrigo means inflammation where skin surfaces rub together, including the armpits. Heat and trapped sweat increase friction and damage the skin. An early rash can look red or reddish brown and feel itchy, burning or sore. More damaged skin can become raw, cracked, scaly, bleeding or weeping. Intertrigo itself is not a fungal infection, but bacteria or fungi can grow in the damaged fold and cause an infection. Candida, a type of yeast, is the most common secondary infection. Treating every underarm rash as yeast misses other causes.3

Contact dermatitis is eczema triggered by a substance touching the skin. An irritant directly damages the skin surface; an allergen triggers an immune reaction. Soap, detergent and repeated contact with water can irritate skin. The rash can be itchy, dry, cracked or blistered. On lighter skin it can look red; on darker skin it can look dark brown, purple or grey. A reaction usually appears within hours or days of exposure, rather than necessarily while you are using the product.4

Fragrance allergy can cause contact dermatitis where personal care products are applied, including the underarms. A deodorant related rash can improve after the deodorant is stopped. Burning, stinging or intense itching can start before the rash becomes visible. Continued contact with the trigger can leave skin thickened, flaky and deeply cracked.5

These patterns are clues, not a way to diagnose the rash yourself.

What should you do first?

1. 1Stop suspected triggers. Set aside a deodorant, soap or other product that appears linked to the rash. Avoiding the substance causing contact dermatitis is the main step toward clearing it.
2. 2Pause shaving until the irritation has gone. Razor burn and ingrown hairs can cause underarm itching, and continued shaving keeps the area exposed to another source of irritation.
3. 3Wash daily and after sweating. For contact dermatitis, use an emollient soap substitute rather than ordinary soap that dries the skin. Avoid repeated washing.
4. 4Dry the fold completely after bathing. Use a fan or a hair dryer on its cool setting if moisture remains.
5. 5Reduce rubbing. Wear loose clothing and fabrics that draw moisture away from the skin. Clean gauze or a dry towel can separate rubbing skin folds.
6. 6Match the next step to the skin problem. A friction barrier helps mild, uninfected intertrigo; a moisturizer helps dry contact dermatitis. Infection needs treatment aimed at the organism causing it.

A cool hair dryer can help dry a damp skin fold, giving a styling tool a less glamorous assignment.2

Should you moisturize or keep it dry?

For mild intertrigo without infection, keep trapped moisture under control and reduce friction. Petroleum or zinc oxide creams and ointments can form a protective barrier. Antiperspirant cream or powder can reduce sweating, but antiperspirants can also irritate underarms. Stop a product that is contributing to symptoms rather than using it to control the sweat.12

Dry contact dermatitis needs moisture in the skin, not lingering sweat in the fold. Test a fragrance free moisturizer on a small area before applying it widely. If tolerated, apply after washing while the skin is still damp, and reapply during the day when the skin feels dry. A pharmacist can help choose an emollient, which is a moisturizer used to prevent dryness.47

How can you calm the itch?

For contact dermatitis, hold a clean towel dampened with cold water against the area for 10 to 15 minutes a few times daily. Calamine lotion or a cool oatmeal bath can also relieve itching and help dry oozing skin. Avoid scratching: it worsens the rash and can lead to infection. These measures relieve symptoms; avoiding the trigger remains necessary for healing.7

Which rash cream should you use?

Antifungals such as clotrimazole or miconazole are options for fungal involvement. Bacterial infection can require a prescription antibiotic cream or oral treatment. A low potency steroid such as hydrocortisone treats inflammation, not the underlying cause of every rash. Stronger steroids are best avoided in skin folds because they can thin the skin and cause stretch marks or, rarely, ulcers. Ask a pharmacist or clinician to help match treatment to the cause rather than choosing solely by how itchy the rash feels.26

How long will it take to clear?

Contact dermatitis usually improves or clears when its trigger is identified and avoided. Persistent, recurring or severe symptoms need assessment rather than repeated changes of cream. Look beyond the newest product: an allergic reaction can develop to something used for years, either because its formula changed or because a new allergy developed. Delayed reactions also mean the last product applied is not necessarily responsible.47

Wash new clothes before wearing them to remove chemical residues and dyes, because 'new' is not a washing instruction.7

When should you see a doctor?

Seek prompt medical care for pus filled bumps, raised tender bumps or a foul smell, which can signal infection. Fever or severe underarm pain also needs medical assessment. Arrange a visit if the rash spreads beyond the fold, worsens, does not resolve with home care, interrupts sleep, or comes with a lump or swollen glands. Diabetes or a weakened immune system increases the likelihood of intertrigo. Tell the clinician about medicines you take, products used on the area, allergies and previous skin problems.123

A clinician can examine the rash and use a bacterial swab or fungal scraping to identify an infection. A special light can help identify erythrasma. An unusual rash or one that fails to respond sometimes needs a skin biopsy, where a small sample is examined. Identifying the cause matters because more than one problem can affect the same fold.26