What is Causing that Rash?

If your skin suddenly breaks out with a red, raised, itchy rash, you may be experiencing an allergic reaction to something that touched your skin.

This can happen even if you have come in contact with the irritant many times before. But now your skin has developed a histamine response to it. It’s possible this contact happened hours or even days before the rash appeared. Left untreated, the rash can spread to other parts of the body.

This allergic reaction is called contact dermatitis. A variety of substances can cause this condition, including certain soaps, cosmetics, fragrances, jewellery, cleaning chemicals, and plants. Your skin comes in contact with so many different surfaces and products every day; it can be tricky to figure out exactly what triggered your contact dermatitis. 

How are rashes diagnosed?

Following the appearance of an unexplained outbreak on your skin, contact your primary care physician or dermatologist. “Tell them about any environmental exposures to chemicals or products and anything you recently consumed, such as food or medications,” says Katlein Paola De Franca, M.D., Ph.D., a dermatologist with the University of Miami Health System. Your doctor will go over your medical history. Then, you will discuss any other symptoms to determine if your rash was caused by something other than contact dermatitis.

Other causes of rash include reaction to a medication, exposure to heat, psychological stress, psoriasis, eczema, and bacterial or fungal infection.

“Always consult your doctor if a rash worsens, is spreading to different areas, shows signs of local infection (like swelling, oozing or pain), and occurs with other symptoms such as fever, swollen glands, sore throat, muscle pain, or difficulty swallowing,” Dr. Franca says.

Once your condition is diagnosed as allergic contact dermatitis, your doctor can refer you to a specialist for a patch test to determine the cause.

What is a patch test for allergies?

A patch test for allergies can help identify the specific cause of your contact dermatitis so that you can avoid the culprit in the future. 

During a patch test, sheets containing small amounts of allergens are taped to your skin, typically on your back. You and your health care provider then monitor your skin’s response over the next two to four days to see if an allergic reaction develops on the skin. Refrain from vigorous physical activity and from getting the test area wet until you’ve completed the necessary series of clinical visits, up to three visits. 

When allergic reactions develop during testing, they appear as small, red, mildly itchy patches beneath the allergen sheets. Each rash patch on the skin is a response to a single allergen. This reveals exactly which substance(s) can trigger contact dermatitis on your skin and the severity of this reaction.

“A patch test may identify allergens not found by an allergy skin prick test or blood test, including chemicals in hair dyes, fragrances, preservatives, toiletries, cosmetics, rubber, and metals,” Dr. Franca says. In about 70% of cases, a patch test performed at UHealth detects at least one contact dermatitis allergen.

This method should not be confused with prick testing, which is usually performed by allergists. Needle prick tests can identify allergens that trigger type I allergies, such as hay fever, asthma, food allergies, and latex allergy. Prick testing involves needle pricking and takes 15 to 20 minutes to get a result.

How are rashes treated?

To help soothe a contact dermatitis rash and calm itching, your dermatologist may prescribe a steroid cream or ointment. You will likely apply the steroid one or two times each day for two to four weeks.

In severe cases, your dermatologist may prescribe oral medication (such as corticosteroids, antihistamines, or antibiotics). These have shown to relieve bothersome symptoms or fight a bacterial infection.

Patch test visits are available on Mondays, Wednesdays, and Fridays at the University of Miami Health System’s Contact Dermatitis, Environmental & Occupational Dermatology Clinic. To schedule an appointment, call 305-243-6704.

Dana Kantrowitz is a contributing writer for UMiami Health News.

Tags: allergies, contact dermatitis, dermatology, Katlein Paola De Franca, patch testing