This article will go over what can cause an armpit rash, as well as how to treat a rash in your armpit.
Allergic Contact Dermatitis
An armpit rash can be caused by an allergic reaction. Allergic contact dermatitis occurs when an allergy-triggering substance (allergen) comes into contact with the skin.
Allergic contact dermatitis does not happen right away (delayed-type hypersensitivity reaction). It’s usually something that happens over time as you become hypersensitized to substances that your immune system sees as foreign.
It can take weeks of being sensitized for a reaction, like a rash, to show up. However, when you come in contact with the trigger again, the rash will show up sooner.
The rash often affects the area the allergen touched and make it look red, raised, and irregularly shaped, as well as cause blisters or crusting.
Your armpit can get sensitized to ingredients in deodorants, antiperspirants, or shaving creams.
If you have an armpit rash from allergic contact dermatitis, figuring out what you’re sensitive to and avoiding it is the first step to healing the rash and keeping it from coming back. When you’re shopping for personal care products, “fragrance-free” formulas will likely help you avoid common allergens.
Your provider can also prescribe treatments or recommend something over-the-counter (OTC) to help with symptoms.
Irritant Contact Dermatitis
Armpit rashes can also be caused by another kind of dermatitis. Irritant contact dermatitis is similar to allergic contact dermatitis, but the reaction is not an allergy. It’s the direct effect of an irritant or toxin on the skin.
Irritant contact dermatitis in your armpit can also be caused by deodorants, antiperspirants, soaps, or body washes. The rash is red, rough, or scaly. In severe cases, it can cause blisters.
As with other kinds of dermatitis, if you have an armpit rash that’s caused by an irritant, the first thing to do is to figure out what’s causing your skin to react. Once you know what irritant is causing the rash, you can avoid it.
If your symptoms are severe or not getting better, it’s important to let your provider know. In some cases, skin reactions may not clear up unless you take a prescription (like a steroid) to help with the inflammation.
Intertrigo
Since your armpit skin folds on itself, it can trap moisture. Intertrigo is a rash that strikes moist areas of skin folds. It’s common in the armpits, under the breasts, and in the folds of the groin and abdomen.
The rash is often caused by yeast, fungi, or bacteria that love being in a damp environment. These germs trigger your immune system to react, which leads to skin inflammation and rash.
The symptoms of intertrigo include:
Roughly symmetrical red or reddish-brown rash with small bumpsItching, stinging, or burningCracks and bleeding if left untreatedFoul smell and pus-containing bumps if it’s infected
Treatment for intertrigo starts by reducing the inflammation and other symptoms, which can often be done with over-the-counter (OTC) products. You may also need antibiotics or antifungals to fight the organisms that caused the rash.
You can prevent intertrigo by keeping your skin clean and dry, and avoiding wearing tight-fitting clothing that doesn’t give your skin a chance to “breathe.”
Erythrasma
Sometimes an armpit rash is caused by a specific germ. Erythrasma is a rash that develops after infection with the Corynebacterium minutissimum bacteria.
Erythrasma is common in the armpits, under the breasts, in groin folds, and between the toes. The rash is reddish and/or tan. It can cause slight wrinkling. It looks coral-red under a black light.
Erythrasma can be mildly itchy but often doesn’t have any other symptoms.
If you get erythrasma in your armpit, you’ll probably need to be treated with antibiotics like erythromycin.
Tinea Corporis
Some common skin infections may show up as an armpit rash. Tinea corporis is commonly called “ringworm," but it’s actually a skin infection that’s caused by a fungus, not a worm.
There are different types of fungi that can cause ringworm and the name of the infection changes depending on where it is.
For example, when it’s in the underarm or behind the knee, it’s called tinea corporis. If it’s on the foot, it’s called tinea pedis (or “athlete’s foot”). When it shows up in the groin, it’s called tinea cruris (or “jock itch”).
The rash from ringworm usually looks red and has raised borders which can have a thin layer of scale on them.
The defining feature of a ringworm rash is that it grows outward in a circle. Ringworm can also be itchy and makes hair fall out.
Ringworm is treated with topical antifungal medications, many of which you can buy over the counter at the pharmacy.
Acanthosis Nigricans
Armpit rashes can also happen from causes that aren’t linked to an infection. Acanthosis nigricans can look like dark, “velvety,” raised patches. It appears in the skin folds of the armpits, groin, and around the neck.
Acanthosis nigricans is linked to increased insulin levels in the blood, which can happen with conditions like:
ObesityDiabetes or insulin resistanceHormonal changesCertain medicationsCancer
It’s not common but sometimes the acanthosis nigricans rash can be itchy.
Acanthosis nigricans is not treated directly. Instead, the condition that’s causing it needs to be treated. Once the underlying condition is under control, the rash should get better.
Summary
Many rashes can occur in the armpits because the skin is thin and damp. Some of the causes are related to skin irritation and allergic reactions, while others are caused by infections or underlying health conditions that need to be treated.
If you have a rash in your armpit, you might not be able to tell on your own what’s causing it. Your provider can diagnose the rash and make sure you get the right treatment.
