Patch testing is a non-invasive skin test to identify possible culprits in cases of allergic eczematous contact dermatitis. At our clinic, 20 to 30 allergens are tested at a time using the Chemotechnique European baseline series imported from Switzerland. These are placed on special IQ Ultra chambers made by Chemotechnique, Switzerland. The IQ Ultra chambers are then applied to the upper back, the most preferred site for patch testing.

The patches are removed with an initial reading after 48 hours. For these 48 hours the back should not be wetted. So one should bathe using a bucket and tumbler instead of showering.Also avoid sweating and heavy lifting, as the patches may come loose.

Some substances can cause late reactions. Hence a second reading on the 4th or 5th day is preferable. Again, till then the back should be kept dry. At the end you get a report of the positive reactions and a list of the source of the potential allergens.

Patch testing may not be able to identify the cause of allergy in each and every case. In our practice, the yield of patch testing is approximately 60%. Very importantly, a negative patch test is helpful in reassuring us regarding the safety of certain suspected allergens. For example, in suspected cases of allergy to hair dye, a negative patch test to paraphenylenediamine can be helpful in deciding whether a patient con continue to use hair dye or not.