Written By: Bhavyajyoti Chilukoti | Updated : February 25, 2015 6:06 AM IST
Most people are allergic to various substances that they tend to use or consume on a daily basis like peanuts, almonds (badam) and eggs. Others can be allergic to hair dyes, mehendi or other products. That's why many of these products ask you to take a patch test, but whatis a patch test?
The patch test is a diagnostic test which can be done at home (to check for allergic reaction against any food or market product) or at a lab (to detect allergy to any specific substance like poison ivy or oak). Once an allergen causing the allergy is identified, avoiding it will help in curing the condition. The kind of allergy that you get when you come in contact with a particular substance is known as contact dermatitis.
How it is done?
At home
It is fairly easy to do a patch test at home, all you need to do is put a small sample of the product (like hair dye or a paste containing eggs or almonds) onto your skin (the skin on the inner side of your arm) and wait for an hour, to check if it causes any reaction or not. You need to perform the test every time you use a new product or any substance which has the potential to cause an allergic reaction.
At the lab
The patch test, when done clinically, involves the use of a paper tape for placement of various chemicals (that might trigger allergic reaction) onto the skin. The tape is then pasted on the person's back. This test is non-invasive i.e., it does not involve use of needles. The tape has to remain on the skin for 48 days (2 days) and care should be taken to not wet the tape (excessive sweating should be avoided and only sponge bath with proper care is advised).
An initial reading is taken after 48 hours by a clinical professional by removing the tape. Prior to removal of the patch, a permanent (or surgical) mark is made on the back where the tests were performed, to take an additional reading after 72 96 hours (3 4 days after initial patch test is done). The person can bathe normally after the final readings are taken.
How to interpret results?
A positive patch test indicates mild swelling, bumps or redness (which means you need to avoid that product and opt for an alternative), and a negative result does not show any allergy-like symptoms; indicating that you can use the product. In people with sensitive skin, a patch test done in the lab (with the use of a tape) may cause minor irritation and itching which does not signify a positive reaction. Although the patch test is commonly performed on the back, it's result do not apply to the skin on the back alone and can be generalised for the entire body. For instance, if the patch test shows that you are allergic to the components present in eyeliner, you will suffer from contact dermatitis on the eyelids, if you use the product. In case you experience any allergic reaction like severe itching or redness during the test, contact your dermatologist at the earliest. Do not apply topical creams or steroid creams without your doctor's recommendation.
Image Source: Getty Images
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