What are they?

Allergy skin tests are tests to find out if a substance, called an allergen, may cause an allergic response. A small amount of a suspected allergen is placed on or below the skin to see if a reaction develops.

There are three types of skin tests:

• Skin prick test. The health professional lightly scratches or pricks your child's skin with a drop of a liquid that contains a possible allergen.
• Intradermal test. Your child gets a shot with a small amount of the allergen solution.
• Skin patch test. A patch with the allergen solution is taped to your child's skin for 24 to 72 hours.

Why are these tests done?

Allergy skin tests are done to find out what things your child is allergic to.

How do you prepare for the tests?

Be sure to tell your doctor about all the medicines your child takes. Your child may need to stop taking some medicines before getting an allergy skin test.

How are these tests done?

For a skin prick test

The doctor will:

• Clean the test area (usually on your child's back or arm) with alcohol.
• Place drops of the possible allergens on your child's skin.
• Prick the skin under each drop with a needle. The needle passes through the drop and allows some of the allergen to go into your child's skin.
• Check your child's skin after about 15 minutes for red, raised itchy areas called wheals. If a wheal forms, it means that your child is allergic to that allergen. This is called a positive reaction.

For an intradermal test

The doctor will:

• Clean the test area (usually on your child's back or arm) with alcohol.
• Use a needle to inject the allergen solution into the skin.
• Check your child's skin after about 15 minutes for red, raised itchy areas called wheals. If a wheal forms, it means that your child is allergic to that allergen. This is called a positive reaction.

For a skin patch test

The doctor will:

• Put drops of solution containing the allergens on patches that look like adhesive bandages.
• Put the patches on your child's skin (usually on your child's back). This usually takes about 40 minutes, depending on how many patches are applied.

Your child will wear the patches for 24 to 72 hours. Make sure that your child keeps the patch area dry when bathing and does not do any activities that could cause a lot of sweating while wearing the patches. This could loosen the patches and cause them to fall off.

After your child has worn the patches for 24 to 72 hours, the doctor will remove the patches and check your child's skin for signs of an allergic reaction.

What happens after these tests?

The results of the skin prick or intradermal test will be available right after the test is done. The results from the skin patch test may be available right away, or when the doctor removes the patches. But a skin patch test reaction might not be seen for up to 2 days after a patch is removed.

If your child has an allergic reaction from any of the skin tests, he or she may have some itching, tenderness, and swelling where the allergen solutions were placed on the skin.

How long do the tests take?

Allergy skin tests usually take less than an hour.