What Can an Allergen-Specific Test Tell You About Atopic Dermatitis?

Medically Reviewed by Stephanie S. Gardner, MD on March 02, 2022
6 min read

Atopic dermatitis (AD) is an inflammatory skin condition. It’s a common type of eczema that usually starts early in childhood. Around 30% of kids who have AD may test positive for a food allergy at some point.

Babies with eczema might develop these food allergies within the first few months.

Research shows that kids who have AD and a food allergy are more likely to have a certain type of eczema. And food allergies might make it harder to control eczema symptoms, especially when AD is moderate to severe. But that’s not the case for everyone.

Some experts think food allergies affect AD in young children more than older kids or adults. But talk to your doctor if your or your child’s eczema symptoms aren’t well-controlled. They’ll help you detect and manage food allergies.

Immunoglobulin E, or IgE, is an antibody your immune system makes to get rid of germs.

It’s natural to have a little IgE in your blood. But your levels can go way up if you have allergies. An allergen-specific IgE test combines your blood with an allergen to see how your immune system reacts.

A lab technician can measure how much IgE shows up in your blood when you’re exposed to certain foods or proteins. You won’t get your results right away. It might take up to 2 weeks.

Any food can cause an allergic reaction. But the most common ones linked to atopic dermatitis include:

  • Cow’s milk
  • Egg
  • Peanut

Some other common food allergies include:

  • Soy
  • Tree nuts
  • Wheat
  • Fish and shellfish
  • Sesame

You don’t need to do anything special to get ready for an IgE test, but it does involve needles. That’s something you’ll want to prepare your child for.

Older kids can have blood drawn from a vein in their arm. If your child is a baby, a health care professional will take blood from their heel. It should only take a few minutes.

An IgE test can’t diagnose you with a food allergy for sure. But it can show you how likely it is that you’re allergic to something. Your doctor will go over your results. Here are some things they might discuss.

Positive test. This is a good sign you’re allergic to that food, but your IgE score alone doesn’t predict how strongly you’ll react to an allergy.

You could also have a false positive. That means the test detects a boost in IgE, but you don’t have a true allergy or any problems eating that food.

Negative test. This means it’s unlikely that a food allergy is causing your AD symptoms. But a negative result doesn’t guarantee that you don’t have an allergy.

Experts recommend testing for limited food allergies in kids younger than 5 years old who have a clear and fast reaction to certain foods or their AD symptoms don’t get better with treatment.

While food allergies seem to be more common in younger children, older kids with a pollen allergy might also get some itching if they eat certain foods, including apples, celery, carrots, or hazelnuts.

Your health provider might also suggest a food-specific IgE test in the following situations:

Your current treatment doesn’t help enough. Whether you’re an adult or a child, your doctor might want to check for food allergies if you’re on a good eczema treatment but you still have poor symptom control.

Other tests are a no-go. Your allergy doctor might prefer an IgE test over other methods for several reasons, including:

  • You can’t stop taking antihistamines
  • There’s a good chance of a serious allergic reaction
  • Your atopic dermatitis is so serious it interferes with a skin test
  • You’ve had a serious allergic reaction within the past month

Food causes a reliable reaction. Both kids and adults with AD can develop food allergies. Tell your doctor if you or your child’s eczema gets noticeably worse after eating only certain foods.

An immediate reaction means your symptoms show up within seconds or hours after a meal or snack.

Common signs of a food allergy include:

Food allergies sometimes cause a life-threatening allergic reaction. That’s called anaphylaxis. Get medical help right away if you or your child have the following symptoms:

The kind of test you get depends on a few things. Your doctor will consider the cost or availability of an IgE test and how serious your food allergy might be. They might also ask what kind of testing you prefer.

Other methods used to check for a food allergy include:

Skin prick test. You’ll have to stop antihistamines for this test. But you don’t need to eat a specific food. This test is safe for babies and adults. A health professional will watch you or your child closely in case there’s a serious allergic reaction.

A doctor or nurse puts a little bit of the suspected allergen on or under your skin, usually on your back or arm. After about 15 minutes, they’ll check for a red bump. It may itch.

A skin prick test can check for more than one allergy at a time. Though, it’s not recommended to screen broadly for foods that don’t cause you any problems.

Oral food challenge. This test is often used to confirm an allergy. You might hear your doctor call it a double-blind-placebo-controlled oral food challenge (DBPCFC).

You’ll eat certain foods in a medical setting. A health professional will watch for and treat any serious allergic reactions. If you want this test, ask your primary doctor to set you up with a specialist who knows a lot about food-related allergies.

Elimination diet. Your allergy doctor might suggest you avoid certain foods for 3 to 4 weeks to see if your skin gets better. They’ll let you know how to safely put these foods back in your diet. When you do, watch for an eczema flare.

Atopy patch test. This might detect delayed, or non-IgE-mediated, food allergies. You’ll wear an allergen patch for about 48 to 72 hours. It’s not a common way to check for food allergies.

The key difference is a true food allergy triggers a specific kind of immune response that affects multiple organs in your body.

Food intolerances are when you have trouble digesting certain foods. For instance, people with lactose intolerance don’t make enough lactase. That’s an enzyme you need to break down a type of sugar in dairy products.

Food sensitivities are less well understood and you can’t test for them. It’s when certain foods cause uncomfortable symptoms even though you don’t have an allergy or intolerance to them. A common example is a non-celiac gluten/wheat sensitivity.

Immediate reactions to an intolerance or sensitivity can be mild or serious, but they’re rarely life-threatening. Some symptoms may overlap with an allergy, including:

But you may also have:

Your doctor will help you decide what’s safe to eat.

In general, it’s best not to eat foods you’re allergic to. But kids might grow out of certain food allergies, and you might find that your or your child’s food sensitivities go down when your AD symptoms are under control.

Always talk to a nutritionist or other health professional before you make any big changes to what you or your child eat. Food changes might improve your AD symptoms, but it’s best to keep your diet as broad as possible.