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Allergic contact dermatitis (ACD) is a rash caused by an immune reaction to various substances that touch the skin.
Allergic contact dermatitis is common, occurring in up to 1 in 5 people. Although anyone can be affected at any age, people with eczema since childhood may be more likely to develop ACD.
Signs and Symptoms
After becoming allergic to a substance, further contact causes itchy, red, and flaky rashes, sometimes with blisters or oozing. Rashes are delayed, usually taking hours or days to appear and weeks to heal. They are most intense at areas of direct skin contact, but may spread. The shape of the rash might hint at its cause, such as streaks from brushing against leaves, or a round patch next to jean snaps. Indirect exposures (eg, substances transferred from one body part to another or carried in the air) can also be involved, causing more widespread reactions. Allergic contact dermatitis can be mildly annoying or severely affect daily life and even the ability to work.
Allergic contact dermatitis is complicated by common misconceptions. New and old products can be responsible, and allergy can develop after using the same product for years. Also, ingredients may be changed by manufacturers over time. The responsible product, contacted as little as once weekly, can cause a constant rash. Additionally, allergy can develop to expensive and natural/organic products. Finally, switching products often does not clear the rash, because similar ingredients may be contained in multiple products.
Common Sources of Allergens
Common sources of allergens include nickel and other metals; personal care products (eg, shampoos, cleansers, moisturizers, deodorants, and sunscreens); cosmetics, nail polish, and hair dye; topical medications (over-the-counter and prescription); plants (most commonly, poison ivy, oak, and sumac); rubber materials (eg, gloves, shoes, elastic in clothing); and plastics and glues.
Many products contact the skin throughout the day, making it nearly impossible to pinpoint the cause of ACD through trial and error. Apart from clear reactions to poison ivy or nickel, patch testing is required to confirm the diagnosis. Patch testing is different from prick, scratch, or allergy blood testing, which cannot diagnose ACD; it does not test for food allergies. A series of patches, each containing a potential allergen, will be applied to your back and then removed 48 hours later. After another 1 to 2 days, your physician will check for reactions to determine if ACD could explain your rashes.
While allergy may be lifelong, dermatitis is not. Allergic contact dermatitis is curable if you completely stay away from the substances to which you are allergic. Your physician will provide information on your allergies, avoidance strategies, and safe products. After making the necessary changes, improvement can take weeks to months. During this time, your physician may prescribe medications to control symptoms.
American Contact Dermatitis Societywww.contactderm.org
American Academy of Dermatologywww.aad.org/public/diseases/eczema/types/contact-dermatitis
Published Online: January 27, 2021. doi:10.1001/jamadermatol.2020.5639
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Adler BL, DeLeo VA. Allergic Contact Dermatitis. JAMA Dermatol. Published online January 27, 2021. doi:10.1001/jamadermatol.2020.5639
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