Shrimp may have always been your favorite indulgence. But one night, after a luscious dinner at a seafood restaurant, you break out in itchy hives or, even worse, find yourself struggling to breathe. What’s the problem?

It could be a food allergy…completely out of the blue. Because food allergies are so commonly associated with children, many adults are shocked to learn that a food that they have enjoyed for decades can suddenly trigger alarming—or even life-threatening—symptoms.

Surprising statistic: In a recent national survey that included more than 40,000 American adults, an astounding 45% of those with a food allergy developed the condition after age 18.

Even though the research showed that more adults are developing new food allergies, science hasn’t yet pinpointed why. Researchers theorize that the uptick could be due to a number of different factors, including changes in our environment…increased hygienic practices…increased exposure to antibiotics or antibacterials…changes to our microbiome (microorganisms, such as bacteria and fungi, in an environment)…and/or overall changes in dietary habits.

CULPRIT FOODS

What food allergies are most common in adulthood? Shellfish tops the list, with just under 4% of study participants reporting that they developed this allergy after age 18. In addition to shellfish, seven other foods (milk, peanuts, tree nuts, fish, eggs, wheat and soy) are responsible for 90% of food allergies in adults and children.

But this list is by no means complete. You can develop a food allergy to many other foods.

SYMPTOMS TO WATCH OUT FOR

How do you know that a food allergy is making you feel lousy—or even putting your life at risk by making it difficult to breathe?

Unlike a food intolerance or sensitivity, which tends to cause milder symptoms, such as abdominal discomfort (stomach pain and bloating, for example), that can occur even a day later, a food allergy triggers symptoms that are acute, more immediate and tough to ignore.

Within a few hours or even minutes of eating the questionable food, you might experience itching, swelling, rash or hives…wheezing, difficulty breathing and/or a feeling that your throat is closing…vomiting (combined with hives or rash)…and even a precipitous drop in blood pressure that can lead to fainting.

Important: If someone is experiencing any of these symptoms due to a known or possible food allergy, it’s imperative for the person to be given epinephrine as soon as possible to reverse an allergic reaction. Call 911 to get medical help. Whether epinephrine is self-administered or given by another person, the treated individual should receive medical care immediately following its use.

GUESSWORK ISN’T ENOUGH

Why are food allergies in adulthood so frequently missed?

The symptoms, of course, aren’t easily overlooked. But what often happens is that the sufferer simply stops eating the problematic food. If shrimp makes you break out in hives, you can just stop eating it, right? (This tactic is why the incidence of food allergies in adults is likely underdiagnosed.) Or you simply may not recognize what is behind some annoying symptom, such as a chronic cough.

But food avoidance—without knowing for sure why the reaction occurred—isn’t always the answer. Getting a proper diagnosis is crucial, because completely dodging a food isn’t always realistic (hidden ingredients, anyone?) and you need to know how to manage the problem in any circumstance.

IDENTIFYING A FOOD ALLERGY

The first step to unearthing a food allergy is to keep a food diary that  documents the food(s) you’re eating that cause symptoms. This will give you an accurate history to discuss with your physician—ideally an allergist,* who has special training in diagnosing and treating allergies. You also can record the information with an app on your phone.

To make an actual diagnosis, your physician may draw from an array of clinical tests. However, it is important that this testing be based on a supportive clinical history after ingestion of an allergen. The different types of testing that are useful in confirming a clinical food allergy are…

• Skin prick tests involve placing a drop of allergen onto the surface of the skin, then pricking it through to introduce the allergen into the top layer of the skin on the forearm or back. If specific immunoglobulin E (IgE) antibody toward the allergen is present and attached to the allergy cells, then redness and an itchy bump should develop within about 15 minutes. Some doctors prefer this type of testing over blood tests (see below) because they consider skin prick tests to be more accurate.

• Blood tests that measure the presence of IgE antibodies to questionable food(s) in the blood.

• Oral food challenge, considered the gold standard to identify food allergies. Increasing amounts of the problematic food are consumed in the doctor’s office, where you’re observed for a reaction in a controlled environment. Note: You do not need the oral food challenge if you get a positive test result from a skin prick or blood test and you’ve had a past reaction to the offending food. Because the blood test and skin prick test have a high false-positive rate, you need both the positive test result and a past food reaction to be considered to have that allergy.

If you’re diagnosed with a food allergy, your allergist will advise you on the foods to avoid and give you coping strategies in case of an allergic reaction. For example, you’ll get a prescription for an epinephrine auto-injector, along with specific instructions on how and when to use it. If you have a known food allergy, you also may want to wear a medical ID bracelet, available online.

On the horizon: Several exciting treatment advances soon may offer other options. These include oral or skin patch–based immunotherapies that slowly release an allergen into the body in small quantities, desensitizing the immune system to its effects…and vaccines to prevent a food allergy from taking hold among those considered at risk.

*To find an allergist near you, consult the American Academy of Allergy, Asthma & Immunology at Allergist.AAAAI.org or the American College of Allergy, Asthma & Immunology at ACAAI.org/locate-an-allergist.