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The cause of a skin rash (dermatitis) can be tough to figure out—even for dermatologists. That’s where patch testing comes in handy, according to leading dermatologist and founder ofAdvanced Dermatology P.C. and The Center for Laser and Cosmetic Surgery PC, Joshua L. Fox, MD. “Patch testing of the skin can tell us if a rash is being caused or exacerbated by an allergy,” he says, “and can help us to distinguish a skin allergy from other skin conditions, such as eczema, irritant dermatitis, or psoriasis.”
Skin allergies occur when your skin comes into contact with substances called allergens. Some people have immune systems that are hypersensitive to these substances. Common allergens include nickel (in jewelry), rubber (especially latex), dyes, preservatives, medications (such as antibiotic ointments), cosmetics and fragrances, and poison ivy, oak, and related plants. When an allergy is to blame, a red, itchy, inflamed rash will appear on the body in the areas where the skin has met the allergen. “If you’re allergic to nickel and wear a necklace that contains this metal, you will usually develop a rash around your neck.” however, if you’re allergic to latex and wear latex gloves, you will usually develop a rash on your hands although you can develop an allergic reaction throughout the entire body and in rare cases can be life threatening,” Dr. Fox explains.
In contrast, the cause of eczema, a chronic skin condition that inflames the skin, causing pain, itching, dryness, swelling, cracking, weeping and scaling, is unknown. In addition, eczema can affect any part of the body, but typically occurs on the sides and back of the neck, and the insides of the elbows, knees and ankles in children and on the hands of adults. “The two conditions can also coexist, and a skin allergy may worsen eczema,” reports Dr. Fox. Recently it was reported that patients with atopic dermatitis have an increased risk of contact allergies. They therefore require thorough patch testing to help them avoid offending allergens. A new service offered by the American Contact Dermatitis Society in coordination with manufacturers through its website for its members allows the dermatologist to tell the patient which cosmetic or other products they can use which does not have allergens.
What is patch testing?
Patch testing is a simple diagnostic procedure performed at a dermatologist office. Small amounts of a number of common allergens are applied to the back and then covered with a bandage. The test is typically left on for two days, and the patient is asked to return to the doctor’s office so as to see which of the allergens, if any, have caused a reaction. Ideally for the best results the clinician may also ask the patient to return again one to several days later to see if there are any additional / new reactions to the allergens or a change in the previously recorded reaction, New patch test regions allow us not to test to many things that previously went undetected like gold.
Before testing, patients should tell their doctors about their jobs and hobbies, since they can come into contact with unique allergens while handling materials specific to these activities. It’s also important to list the cosmetics and toiletries they use, in case they are the source of the rash. That way, testing can be customized to an individual patient’s exposures. In addition, recent trips or other unusual activities should be stated.
“Before patch testing, patients should not use any oral antihistamines or topical corticosteroids, such as hydrocortisone or other creams, lotions, or ointments, on their backs for 1 week, and they shouldn’t expose the area to the sun,” advises Dr. Fox. While the patch test is on the back, measures should be taken to avoid getting the panel wet while showering or some of the test substances may be washed away. It’s not uncommon to experience itching and burning in the test area after the allergens are applied, according to Dr. Fox, but patients should try not to scratch the skin, as that can inflame it and make it difficult to interpret the test results. “If these symptoms become severe, the doctor should be contacted for guidance,” he adds.
Treating skin rashes
Topical steroid creams and/or oral antihistamines & emollients can often be enough to make a mild allergic skin rash disappear, says Dr. Fox. “More severe cases may need to be treated with oral or injected corticosteroids, or other drugs that can reduce inflammation and stop the allergic reaction.” Other agents utilized include Protopic®, Elidel®, Mimyx® and Atopiclair. Of course prevention is the best course. “Once a patient knows he or she is allergic to something, avoid that allergen at all costs to prevent the rash from recurring often in a more severe presentation. A patient must avoid at all costs something he or she is allergic to, in order to prevent the rash from reoccurring often more severely then the fist time.