Patch Testing For Allergies

Before using any cosmetic on your skin you must take a patch test.  Patch testing is a technique to identify whether a substance coming in contact with the skin is causing inflammation of the skin also known as contact dermatitis. Irritant contact dermatitis and allergic contact dermatitis are the two types of contact dermatitis.

Irritant contact dermatitis is caused due to an irritant substance. An irritant substance causes inflammation in almost every individual if applied in sufficiently high concentration for long period. An irritant reaction is caused when the irritant substance comes in direct contact with the skin. It does not involve the immune system.

Allergic contact dermatitis is due to allergy. An allergic reaction is specific to an individual and to a substance called an allergen. Allergy is a hypersensitivity to a particular substance. Allergy always involves the immune system. Rashes are developed in all areas of the skin that are in contact with the allergen. Patch test is done using various test substances to the skin under adhesive tape. These adhesive tapes are left in place for 48 hours. The skin is examined for any reaction after 48 hours. Based on the skin’s reaction your doctor decides which allergens you are allergic to.
 
Patch testing is the only way to know whether a substance is causing or aggravating your dermatitis. Once an allergen is identified, avoid it to cure your dermatitis. Your dermatologist will suggest which allergens you should be tested for. European Standard Battery is the standard selection of allergens, which consists of the commonest allergens.
Patch testing should be done on a skin site where the dermatitis is not apparent. Mix the allergens with a non-allergic material to a suitable concentration. Then place the mixture in direct contact with the skin, usually on the upper back, within small aluminium discs. Use adhesive tape to fix them in place and mark the test sites. Leave the patches for 48 hours. During these 48 hours don’t wash the area or play vigorous sport because if the adhesive tapes peel off, the process will has to be repeated. Don’t expose the patches to sunlight or other sources of ultraviolet light.

Results of patch test are interpreted as per the International Contact Dermatitis Research Group system, as follows:

• +? = doubtful reaction: This indicates mild redness only.
• + = weak, positive reaction: This indicates red and slightly thickened skin.
• ++ = strong positive reaction: red. This indicates swollen skin with individual small water blisters.
• +++ = extreme positive reaction: This indicates intense redness and swelling with coalesced large blisters or spreading reaction.
• IR = irritant reaction. This indicates red skin. Improves once the patch is removed.
• NT = not tested.