Patch Testing
What is patch testing?
Patch testing is a common diagnostic procedure used to test for skin allergies to determine the cause of your contact dermatitis. Patch testing looks for reactions to substances that come into physical contact with the skin, for example:
- Chemicals
- Metals
- Preservatives
- Soaps
- Detergents
- Fragrance
- Topical Medications
- Plant Resins
What is allergic contact dermatitis?
Allergic contact dermatitis is a condition that develops in response to contact with something that triggers a skin reaction (an allergen).
Why is patch testing used?
Patch testing is done because allergic contact dermatitis is potentially curable, and the goal is to identify and avoid triggers that cause the condition to flare. Also, allergic contact dermatitis can worsen other skin conditions.
The occurrence of allergic contact dermatitis is high in people with eczema or atopic dermatitis. Patch testing is the standard for diagnosing allergic contact dermatitis. According to studies *, one third of eczema patients with therapy-resistant atopic dermatitis may benefit from patch testing.
What is atopic dermatitis?
Atopic dermatitis (AD) is a severe form of Eczema. People with AD have a propensity for allergies. The cause is not known but involves genes and environmental factors. There is no cure.
AD is chronic and flares regularly-causing red and itchy skin. People with AD often also have asthma, hay fever or other allergic conditions. Known triggers for AD include allergens like poison ivy, jewelry, hair care products, stress, dry skin and irritants like soaps, detergents and household cleaners.
Who is at risk for allergic contact dermatitis?
Recent studies** show that the likelihood of allergic contact dermatitis is greater in adults and children with atopic dermatitis than in healthy individuals. Much of it is coming from the use of personal care products to treat atopic dermatitis.
Some identified allergens include:
- Nickel, a metal sometimes used in jewelry alloys, gold and silver
- Lanolin, used in moisturizers
- Fragrances
- Neomycin (Neosporin), a commonly used over-the-counter topical antibiotic
- Bacitracin, a commonly used over-the-counter topical antibiotic
How is patch testing done?
It is a painless and simple office procedure. A postage – stamp sized patch with a suspected allergy-causing substance is placed on the skin of the back and worn for 48-72 hours. The patches must be kept dry to get an accurate reading. The patient returns, the patches are removed, and the doctor looks for signs of an allergic reaction. Typically, 60+ patches of substances that cause contact dermatitis are applied to the skin for a comprehensive, full panel skin allergy test. You will receive complete instructions when Dr. Higgins orders patch testing for you.
What does a positive patch test mean?
A positive patch test indicates an immune system reaction including redness, blisters, itching, rashes, hives and burning. These symptoms are then treated with topical creams to reverse the reaction. Once Dr. Higgins determines what the patient is reacting to, she can recommend personal care products that will not cause allergic contact dermatitis and provide the patient with a list of safe ingredients and things to avoid.
References
* J Eur Acad Dermatol Venereol.2019 Oct;33(10):e377-e378. doi: 10.1111/jdv.15672. Epub 2019 May 26.
** Journal of the American Academy of Dermatology. 2018 Dec;79(6):1028-33.e6
https://www.jaad.org/article/S0190-9622(18)32316-8/fulltext
