What’s skin prick testing for allergies?

A skin prick test can look for common allergens such as house dust mite, certain tree and grass pollens, certain food allergies (the list is long, from particular nuts to fruits and white fish or seafood), milk and egg allergies, animal dander, latex and bee or wasp venom.

It really helps if you can be specific about what you think you are allergic to, so tests can be tailored to you.

A blood test, known as a RAST IgE test, is used in some cases as an alternative to skin prick testing. But results are much slower - they can take up to 4 weeks to come back.

While skin prick testing is useful for certain allergens in the air or in food, and usually causes a near-immediate reaction, another type of allergy testing called patch testing is used for substances that might cause specifically skin reactions – either allergic contact dermatitis or eczema. This reaction on patch testing takes a couple of days to emerge, so-called delayed hypersentiivity reaction, and tests for susbtances that direct contact with the skin.

This procedure involves putting a drop of allergen, at a weak concentration, on your arm and then using a very fine needle to make a tiny prick the skin. The inside of the forearm is usually used, and 10 or 12 different allergens may be applied. You are monitored for 15 to 30 minutes, and any reaction is inspected.

A positive result is if you get an itchy red bump to a particular allergen. Another form of positive reaction is a wheal, a white bump with a red centre. If your skin looks normal, this is considered a negative response.

This is a fairly quick procedure and most people say it’s not so much painful as just a bit uncomfortable.

If you usually take antihistamines, make sure you don’t take these for a couple of days before testing, as these may mask positive results.

This is considered a safe test, as potential allergens are used at very low concentrations and in a small amount. The worst you can expect is an itchy bit of skin for a couple of hours.

If you’ve had any severe allergic reaction in the past, anaphylaxis or you have severe asthma, it’s likely you will be given skin prick testing in a clinic with resuscitation facilities and monitored closely, just to be on the safe side.

The only other risk is that the results are difficult to interpret. There’s a medical adage that if you test for something, you should be ready for the answer. Tests don’t always confirm what you think – a substance you think is definitely causing a reaction may not get a positive result. And something you thought you were fine with may actually prove positive in testing. How do you interpret this? That’s for your specialist to discuss, but your own experience usually trumps allergy testing results.

There are private clinics that offer skin prick testing – dermatologists or allergists are the medical specialists for this area of expertise. Other non-doctor private clinics also offer skin prick testing and other types of allergy testing.

Your GP may consider referring you to an allergy, dermatology or respiratory clinic if you have symptoms that are not easily controlled with standard medications, or you have had a severe reaction, such as anaphylaxis or severe asthma.

It may be enough to know your triggers and avoid them, but if there is a serious risk, you may be encouraged to wear a Medic-Alert bracelet and to carry an EpiPen containing adrenaline for emergencies.