This test is performed in cases of contact dermatitis (Eczema) or any other allergy is suspected. The allergens are prepared in appropriate concentrations in white soft paraffin (e.g. Vaseline) and are then spread on to discs, 1 cm diameter. The discs (which are made of a special metal, cannot themselves provoke a reaction) are placed on the skin, usually on the back, and are kept in place by hypoallergenic tape. The skin is coded appropriately and the patient is asked to keep the skin dry. The patches are left in place for 48 hours.
How is Patch Testing Performed?
Strips of tape containing small quantities of common allergens will be applied to the skin of your back during your first visit.. The allergens must remain in place and be kept dry for 48 hours.
After the 48 hours, the patches will be removed and an initial reading will be performed. The patch sites w/ill be outlined with a marker, and you will be asked to return for a final reading on another day. A positive test will show a red, raised area of skin, often with itching. A strong reaction could cause blistering and, very rarely, a prolonged reaction (lasting several weeks) or scarring.