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Skin or blood tests, when combined with a doctor’s examination and your medical history, can help determine if you’re truly allergic to something you inhaled, touched, or ate. But if you don’t have symptoms or a medical evaluation that points to an allergy, you should think twice about testing. Here’s why.

Random allergy testing usually doesn’t help.

You can now get allergy tests in places outside the doctor’s office. Many drugstores and supermarkets, for example, offer free screenings. And you can even buy kits to test yourself at home. But random allergy testing may detect responses in people who don’t have the same reaction in everyday life. In addition, screenings for food allergies sometimes use a blood test for a protein called immunoglobulin G (IgG). But those allergies are related to a different protein, IgE, and the usefulness of the IgG test to detect food allergies is unproven. Finally, allergy testing usually doesn’t help people who have chronic hives—red, itchy, raised areas of the skin that last for more than six weeks—since those rarely stem from allergies.

Unnecessary tests can lead to unnecessary changes in your lifestyle.

You might give up certain foods, such as wheat, soy, eggs, or milk, end up with nutritional problems, and be unnecessarily worried when dining out or buying groceries. A mistaken warning about allergy to pet dander might make you give up your dog or cat. And an aggressive workup for hives may show abnormalities that are unrelated to the condition but lead to anxiety, more tests, and referrals to specialists.

The wrong test can be a waste of money.

Inappropriate tests won’t help diagnose your problem or improve your treatment, and can be expensive. Depending on the number of sub- stances tested, a skin allergy test may cost $60 to $300, and a blood test $200 to $1,000. An IgG blood test can cost hundreds of dollars, and might not be covered by your plan. An extensive evaluation for chronic hives can cost thousands.

So when is testing warranted?

If symptoms don’t improve with self-help steps and over-the-counter drugs, see a doctor for the right test. If your history suggests an allergy, your doctor might recommend a referral to an expert in allergy or immunology for testing. Skin testing involves pricking your skin with a tiny amount of the potential allergen. An IgE blood test can make sense if you have a rash or take a medication that interferes with skin testing. For chronic hives, specific tests usually aren’t necessary, though your doctor might order tests to rule out non-allergic causes, such as thyroid disease, lymphoma, or lupus.

07/2012