A range of substances might aggravate your rash. Patch tests are done to find the cause or aggravating factors for these rashes and are not the same as a skin Prick Test, which are used to diagnose hay fever allergy or food allergy. In Patch tests, strip of patch are applied on the back of the patients with dermatitis (Rash), to find out whether their skin condition may be caused or aggravated by a contact allergy. A range of substances can be used for patch testing. We used the “North American Series” and any specific substance brought by patient to test (if they are safe to apply on back for some time). Patch tests do not always explain the cause of rash but if they are positive they help in making a diagnosis.
On first appointment tiny quantities of 25 to 45 materials in Individual Square plastic or round aluminum chambers are applied to the upper back. They are kept in place with special hypoallergenic adhesive tape. The patches stay in place undisturbed for 48 to 72 hours. The testing generally takes about 1/2 hour to complete but the visit will be for an hour.
If you have a specific sensitivity to any of these substances, it will consist of any of following: erythematous rash, follicular rash, pustules rash and burn-like reactions to skin. A strong reaction can cause blisters and ulcer formation. So it is recommended to remove the specific chambers immediately. Applying hydrocortisone cream to the site will bring some relief. Please note that this reaction may leave permanent scar on the skin.
At the second appointment, usually 2 to 3 days later, the patches will be removed and read. If needed patch is read again at the 3rd appointment, usually 2 days later (4 days after application).