Skin prick testing is a simple, safe and quick test used to help diagnose allergies. The test itself takes around 10 minutes, with results available after about 15 minutes.
A drop of the suspected allergen (the possible cause of your symptoms) is placed on the skin. A small prick is then made using a lancet. If you are sensitive to the allergen, a small raised bump (weal) will appear at the test site, similar to a nettle sting. This may be itchy and surrounded by redness (flare).
A positive result usually means you are sensitive to that allergen. However, results must be considered alongside your symptoms, as some people may have a positive test but no reaction when exposed to the allergen.
A negative result (no weal) usually means you are not sensitive, although false negatives can occasionally occur.
What allergens can be tested?
A range of prepared solutions is available for common food and airborne allergens. If a suitable solution is not available, fresh food may sometimes be used. In this case, the lancet is first used to prick the food before being applied to the skin.
Several allergens can be tested during the same appointment. The selection is based on your symptoms and agreed with your healthcare professional.
Control samples are also used to help ensure the results are reliable.
Are there any risks?
Skin prick testing is generally very safe and usually causes only mild discomfort or itching. Any reaction normally settles within 30 minutes.
There is a very small risk of a more widespread reaction. For this reason, testing is always carried out by trained healthcare professionals in a clinical setting with appropriate support.
The test may be postponed if you are unwell, particularly if you have breathing symptoms such as wheezing.
What to avoid before the test
Antihistamines can affect the results and should be stopped before testing:
- Long-acting (non-drowsy) antihistamines (e.g. cetirizine): stop 1 week before
- Short-acting antihistamines (e.g. chlorphenamine): stop 48 hours before
How is the test performed?
Testing is usually carried out on the inner forearm, although other areas (such as the back or thigh) may be used if needed. A skin marker is used to label each test area. A drop of allergen solution is placed on the skin, and a sterile lancet is used to gently prick through it.
After each test, the excess solution is removed. Once all allergens have been applied, you will wait around 15 minutes. The healthcare professional will then check your skin, mark any reactions, and record the results. These will be measured, explained to you, and discussed alongside any next steps or treatment.
