Glycerin Reaction During Allergy Skin Testing

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A skin-prick test is the go-to test for allergies, but sometimes it's not possible to have that test done. In most cases, this is because of a pre-existing skin disorder, fear that one of the extracts used for testing may set off a super-severe reaction, or a lack of cooperation (such as with someone deathly afraid of any sort of needle or lancet). But in other cases, the discovery that you can't complete the skin-prick test is sudden—and usually unwelcome—as it only becomes apparent after the nurse or doctor has started applying lancets and pricking your skin. However, it's important to understand why the problem may have occurred because that will direct future tests.

Super-Sensitive Skin

If you've got very sensitive skin, you could experience difficult-to-read reactions that don't puff up as nicely and neatly as they should. This can give you false positives, as well as show slight reactions to the glycerin control. This glycerin control is supposed to show the doctor what a reaction to a lancet would look like on your skin without any allergens. That gives the doctor something to compare the other test spots to, in order to determine reaction type. It may be possible to repeat the skin prick test on another part of your body (for example, testing only a few extracts on your arm, which might not react as badly as the skin on your back).


Dermatographia is a poorly understood skin condition in which touch causes raised welts. Sometimes the reaction is so quick that you can actually write on your skin and create raised, legible words. If you know you have this condition, you won't be given a skin prick test in the first place, but sometimes it's not so clear that you have it until you take the test and have a reaction to the glycerin. Often, with mild dermatographia, you don't really have the skin-writing aspect, but you end up having the same reaction to the glycerin as you do to the other lancet spots—in other words, a bad one, but one that is indistinguishable from the allergen extracts. In cases like this, a RAST blood test is the alternative.

Glycerin Allergy

You're really not supposed to be allergic to glycerin—there's a reason it's used as a control—but it is possible to be allergic to anything. If that's the case, either a RAST blood test, or possibly a saline-based skin test (instead of the glycerin-based test) might be possible.

If you're worried that the skin prick test will be impossible, talk to your allergist and see if there's a way to test for any glycerin reactions before undergoing the entire allergy lancet panel. Most people won't have to worry, and your allergist will be able to explain why he or she thinks you'll be fine. to learn more about allergy testing, contact a doctor at a location such as Dino Peds.