Patch Testing

Why is Patch Testing Done?

Patch testing is a technique used to diagnose the cause of allergic contact dermatitis. 

Some people develop skin allergies following repeated contact with certain chemicals or substances.  These chemicals or substances are often found in cosmetic or toiletry products, clothing or jewellery. 

Some people develop contact allergies to workplace exposures.

Patch testing will allow for identification of skin allergies to common contact sensitizers, so that future exposures may be avoided.

How is Patch Testing Done?

Panels of common skin sensitizers (ie chemicals or substances that commonly cause contact dermatitis) are applied as adhesive patches to the skin.  Often patch testing is done on the upper back, sometimes on the upper arms.

Patches are left in place for 72 hours (ie 3 days) and then removed for interpretation.  The first visit to apply the patch tests typically takes a few minutes.  The second visit is a bit longer, about 30 minutes, to interpret results.

Patch tests are usually applied on Mondays and removed on Thursdays, or applied on Tuesdays and removed on Fridays.

Patch tests must be kept clean and dry, precluding baths or showers.  However, sponge baths are permitted.