Delayed reactions to skin testing

January 30, 2003

Skin testing results for inhaled allergies as well as food testing are usually read about 15 minutes after testing. Some tests, such as TB skin tests, or patch tests for contact allergies are read 24 to 72 hours after the test.

The allergists I've worked with have felt that while there may be some significance to a delayed reaction to allergy skin testing, it does not indicate something that can be treated with allergy injections.

The type of allergy treatable by allergy injections is know as Type I sensitivity. This usually involves allergens that cause an immediate reaction of runny nose, watery itchy eyes, an asthma attack, or in some cases hives or a rash. This type of reaction is also known as an immediate hypersensitivity reaction, or an IgE mediated reaction.

While most people do not have a delayed reaction to allergy testing, it occasionally does happen. Some of the tested areas may grow and become itchy for two or three days. They may remain visible for a week or ten days, but usually disappear by that time. This is more common with intradermal (needle) testing than the prick or scratch testing.

Occasionally with intradermal testing, especially when a large number of tests are done, the entire area surrounding the tests will become pink and feel warm. They may be sore or a little achy. This usually subsides in a couple days. We advise our patients to use ice packs and Tylenol should this occur.

Always let your physician know of any delayed reaction. Redness, warmth, and swelling are also signs of infection, so your physician needs to oversee any reaction of this sort. I've done many allergy tests through the years, and I've never known of an allergy test actually causing an infection. But it is not impossible that this could happen. Anytime the skin is punctured, it is possible that bacteria can be introduced into the skin.

Delayed hypersensitivity tests are usually done to test for exposure to TB or other infections, to test for skin contact allergies, or to test the health of the immune system (Anergy testing).

If your test showed allergies to several of the itmes tested for (skin reactions within approximately 15 minutes), it is possible the extra load of allergens could have triggered a slightly increased amount of congestion. This would be more likely if you were exposed to the items you are allergic to immediately before and after testing.

Another possibility is that you are developing a cold or a sinus infection. You should discuss this with your physician. If she believes this is an allergic response to the testing, she may give you an antihistamine. If you are developing a sinus infection, she will probably prescribe an antibiotic.

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