If you have allergies, you’re not alone. More than 50 million Americans have allergies, making them the sixth most common cause of chronic illness. But it’s not enough to know that you’re one of the millions who suffer. To treat allergies more effectively, you first need to know what is causing your allergic reactions. Allergy tests are quick and painless ways to find out. Here’s what you need to know about allergy tests before you head to the appointment.

What allergies and allergy tests are
Allergies are the immune system’s response to certain triggers, called allergens. There are a few types of allergies: seasonal allergies like pollen and some types of mold; perennial allergies, which are commonly caused by dust mites, and cat or dog hair; and food allergies. Wheat, eggs, milk, peanuts, tree nuts, soy, fish and shellfish are the most common sources for food allergies, but any food can be an allergen.

If you want to know your specific allergens, you’ll need an allergy test. There are two types: skin tests and blood tests. “Both are equally valid and very good at detecting allergies, and, overall, are considered comparable tests,” says Christopher Webber, MD, an allergist with Sky Ridge Medical Center in Lone Tree, Colorado.

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How allergy tests are done
Though both tests are simple and accurate, the blood test is more convenient. According to Dr. Webber, a blood test can be done in your primary doctor’s office at any time of the day, doesn’t require an empty stomach and you don’t need to stop taking allergy medications. The drawback is that the test results take longer to process: you’ll receive them within a week, says Webber.

A skin test must be done at an allergist’s office, according to Weber, and you can’t take antihistamines for five to seven days before the test—but you’ll have the results in about 20 minutes. Webber explains the process: an allergist will rub pieces of plastic that have been dipped in various allergens—foods, pet dander, or pollen from different trees, grasses, and weeds—on your back.

A positive skin test will cause a hive or welt that lasts for about 20 minutes. It doesn’t hurt, says Webber. “It is usually very fast, sometimes feels like a small poke that is barely noticeable, does not cause bleeding, and is tolerated at all ages,” he says. “But it does itch. Everyone is worried about the hurt, but forgets the itch.”

False negatives and false positives
Webber says that there are two situations that could cause either a false negative or a false positive in an allergy test, and it’s an allergist’s job to interpret the results of the test. About one in four people with seasonal allergy symptoms don’t actually have allergies; instead, they have irritant rhinitis (also called nonallergic rhinitis), which has many of the same symptoms as allergies but the immune system is not involved. Triggers include cigarette smoke, strong smells, dust, and air pollution, according to Weber. An allergy test could come up negative, but that doesn’t mean a person doesn’t have symptoms, he says.

On the other hand, testing for food allergies can sometimes cause a false positive. That means there’s an immune system response to the allergen, but there are no symptoms. “The test correctly measures the presence of an allergy antibody, but an allergy is the presence of allergy antibody plus symptoms,” Webber says. “Having a positive test does not, by itself, mean you have an allergy.”

What you can do about allergies
Once you’ve received your test results and you know what’s causing your allergic reactions, how do you manage your allergies? For food allergies, simply avoid the allergen and keep an EpiPen ready in case you come in contact with it.

For seasonal allergies, the first step is tracking the pollen count, so you know when to expect symptoms. When the pollen count is moderate to high, Webber says to:

Keep your house windows closed so pollen doesn’t get in.
Shower at night, so pollen doesn’t move from your hair to your pillow while you sleep.
Exercise inside instead of outside.

Webber also recommends changing your air filters every one to three months. Don’t bother with an expensive “allergy-free” filter. Getting cheap ones and changing them often usually yields better results.