Allergy & immunology · Cincinnati
Contact dermatitis and patch testing
An itchy rash where something touches your skin may be contact dermatitis. Dr. David I. Bernstein evaluates patients with allergic and irritant contact dermatitis, at work and at home, and co-authored the national practice parameter on contact dermatitis.
What contact dermatitis is
Allergic contact dermatitis is a delayed allergic reaction: the rash appears one to three days after the skin touches a substance you have become allergic to, such as nickel, a fragrance or a preservative. Irritant contact dermatitis is direct damage to the skin from frequent washing, chemicals or friction, and is the most common type.
Both are common on the hands, face, eyelids and wherever products or materials touch the skin. Finding the exact cause is the key to clearing the rash, because creams only help while the exposure continues.
Common causes
- Nickel and other metals in jewelry, belts and phones
- Fragrances and preservatives in skin and hair products
- Hair dye and nail products
- Rubber chemicals in gloves
- Topical antibiotics and other medicines applied to the skin
- Cleaning products, cement and metalworking fluids at work
How patch testing works
Patch testing is the standard test for allergic contact dermatitis. It is different from the skin-prick tests used for hay fever and food allergy.
Patches applied
Small amounts of common allergens are placed on your back under tape. You keep the area dry.
First reading
About 48 hours later the patches are removed and the skin is checked.
Final reading
A second reading a day or two later catches delayed reactions.
Avoidance plan
You receive a list of the substances to avoid and of products that are safe to use.
Common questions
Is patch testing the same as allergy skin testing?
No. Skin-prick testing checks for immediate allergies such as pollen or food. Patch testing checks for delayed allergies that cause contact dermatitis.
Can I take my usual medicines during patch testing?
Most medicines are fine, but oral steroids and steroid creams on the back can affect results. The office will tell you what to stop and when.
Can a rash be caused by my job?
Yes. Health care workers, hairdressers, machinists, construction and food workers are among those at higher risk. Testing can identify the cause and help with workplace changes.
Will the rash go away?
Once the cause is identified and avoided, most allergic contact dermatitis clears within weeks.
Dr. Bernstein’s work
Dr. Bernstein co-authored the 2015 national practice parameter on contact dermatitis and has written practical guidance for allergists on evaluating contact dermatitis and performing patch testing.
Selected publications
- Fonacier L, Bernstein DI, Pacheco K, et al. Contact dermatitis: a practice parameter-update 2015. J Allergy Clin Immunol Pract. 2015. PubMed · DOI
- Bernstein DI. Contact dermatitis for the practicing allergist. J Allergy Clin Immunol Pract. 2015. PubMed · DOI
- Schmidlin K, Sani S, Bernstein DI, Fonacier L. A hands-on approach to contact dermatitis and patch testing. J Allergy Clin Immunol Pract. 2020. PubMed · DOI
- Caperton C, Bernstein DI. Contact dermatitis. J Allergy Clin Immunol Pract. 2017. PubMed · DOI
A rash that keeps coming back?
Request a consultation. Dr. Bernstein reviews every request personally.