How Are Environmental Allergies Diagnosed?

About 1 out of every 5 people in the United States are diagnosed with environmental allergies. Two out of every 3 people with asthma also have environmental allergies. While these conditions are common, it is still important to get an accurate diagnosis.1

Knowing what you are allergic to helps you know what to avoid and how to manage your particular allergies.

Most people go to their primary care doctor first to get help for their allergies. However, to find out exactly what you are allergic to, you will need to see an allergist. Allergists have special training in diagnosing and treating allergies.1

What tools are used to diagnose an allergy?

Your doctor will use 3 methods to diagnose an environmental allergy. Together, they help your doctor rule out or confirm that you are allergic to something. These tools include:2-4

  • Taking a medical history
  • Conducting a physical exam
  • Ordering various allergy tests

Medical history and physical exam

Your doctor will begin by taking your medical history. It will help your doctor if you come into the appointment with a list of symptoms and some ideas of what you believe you may be allergic to. Jot down your symptoms and when they occur, and things that make them worse or better.

If you have a family history of any illnesses, allergies, or asthma, let your doctor know. Be ready to tell the doctor about any drugs and supplements you take, your diet, and your lifestyle at home, work, and school. All of this information can paint a broader picture of your health and any potential allergies.

The doctor will also conduct a physical exam. They will look at your skin, eyes, ears, and throat, and listen to your breathing. Then, they may order blood tests, skin tests, or X-rays.

Sometimes, the doctor will ask you to keep a symptom diary if they suspect an allergy but need more information from you.

Skin tests

Skin tests can provide your doctor with more information about a suspected allergy. There are 2 different kinds of skin tests: a skin prick test (SPT) and intradermal test. Both offer results during your office visit.3

It is important to remember that, by itself, a positive skin test does not confirm an allergy, nor does it predict the severity of your allergy. However, a negative skin test is highly accurate and usually means you are not allergic.3

SPTs involve putting a small amount of the allergen on your skin and allowing it to seep in. After about 15 minutes, the doctor or nurse will check for any redness, swelling, or itching. Sometimes a hive-like bump (wheal) will appear. Usually, the larger the wheal, the more likely it is you are allergic to the substance. But the size of a wheal does not predict the severity of your allergy.3

An intradermal skin test involves injecting a small amount of the potential allergen into the outer layer of skin. After about 15 to 20 minutes, the area is checked for any reactions. This test may be used if the SPT was negative but allergies are still suspected. It is often used to diagnose drug or insect venom allergies.3

You will need to stop taking antihistamines for some time before the test because these drugs can affect the results.3

Blood tests

Skin tests are preferred because these are more sensitive than blood tests. However, blood tests may be used if you are taking drugs that can interfere with skin tests or if you have a skin condition that makes a skin test hard. Some people who have had severe reactions to skin tests in the past may need to have bloodwork done instead.3

In a blood test, a blood sample is taken and sent to a lab. The lab adds the allergen to your blood sample. They then measure the amount of antibodies your blood makes to attack the allergens. This test has a high rate of false positive results and should not be used as the only tool for an allergy diagnosis. Results usually take several days.3

Why an accurate allergy diagnosis is important

Accurate diagnosis of your environmental allergies is important. In order to fully treat your symptoms, the allergen needs to be identified. Finding which allergen is causing your immune system to react allows you to treat and prevent your symptoms.

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Written by: Jaime R. Herndon | Last reviewed: March 2022