Skins tests are used to find out what might be causing an allergic reaction. Substances that may cause an allergic reaction are called allergens.
Skin tests are often used to find out if a person has an allergic condition such as:
- Hay fever (allergic rhinitis)
- Allergic asthma
- Dermatitis (eczema)
- Food allergies
- Penicillin allergy
- Allergy to the venom of bees and other insects
- Latex allergy
The most common skin tests for allergies include:
- Skin prick or scratch test.
- A small amount of a possible allergen is put on the skin.
- The skin is then pricked or scratched so the allergen goes under the surface of the skin.
- A healthcare provider watches closely for redness, swelling, or other signs of infection. This usually takes about 20 minutes.
- Intradermal (in the skin) skin test. This test is often used to find out if a person is allergic to bee venom or to penicillin. It may also be used to check for a false negative—when the skin prick test comes out negative but the healthcare provider still thinks there may be a skin allergy.
- A small amount of an allergen is injected into the skin.
- A healthcare provider watches closely for redness, swelling, or other signs of irritation. This usually takes about 20 minutes.
- Patch test.
- Possible allergens are taped to the skin for 48 hours (2 days).
- After 3 to 4 days (72 to 96 hours), a healthcare provider looks at the area to check for signs of infection.
Skin tests are usually safe for people of all ages, including children and infants.
There’s a very small chance that an allergy test could cause a severe reaction. For this reason, it’s important to have skin tests done by a healthcare provider trained in emergency treatment of severe reactions.
A healthcare provider may advise against skin testing for people who:
- Have ever had a severe allergic reaction.
- Are at high risk for a severe allergic reaction. This includes people who have asthma that is not well-controlled.
- Take medicines that could interfere with the results. These can include some antihistamines, antidepressants, and heartburn medicines.
- Have a skin condition that covers large areas of the back and arms. There may not be an unaffected area to do the skin testing.
For people who should not have a skin test, blood tests can be an option. Blood tests are used less often because they are more likely to miss positive result. They are also more expensive than skin tests.
The most common side effect of skin testing is swollen, red, itchy bumps. These may start within a few hours after testing and last a few days.
Before testing, a healthcare provider will ask about your lifestyle, eating habits, where you live and work, and your overall health.
You may need to stop taking certain medicines before your skin test. If so, your healthcare provider will tell you what to stop and when.
If the skin does not change in response to the substance, the results are negative (normal). In most cases this means you are not allergic to the substance. In rare cases, a person can have negative results and still be allergic. This is called a false negative.
If the skin gets a red, swollen area (called a wheal [weel]), the results are positive. This usually means the reaction is caused by the substance. Some people can have a positive reaction to a skin test but not have a problem with the substance in daily life.
Based on your symptoms the results of your skin test, your healthcare provider will recommend lifestyle changes to help you avoid whatever is causing the problem.