Contrary to popular belief, not all food allergies develop during childhood. Despite being relatively uncommon, it’s possible for adults to develop allergies to foods they’ve been eating comfortably for decades.

"I was diagnosed at 44 years old," said one MyFoodAllergyTeam member. "It has been awful!! I am allergic to soy and gluten." Another member wrote, "I started having food allergies in my 20s. And the number of allergies has grown quite a bit over the years."

If you suspect you or a loved one may be developing a food allergy, read on to understand why this may have happened, along with tips for navigating life with food allergies.

How Common Are Adult-Onset Food Allergies?

Adult-onset food allergies aren’t as common as those that develop in childhood, but they may be less rare than you’d think. One study found that about 27 percent of people with food allergies didn’t develop their allergies until they were adults. In addition, about half of adults with existing food allergies developed at least one new food allergy after the age of 18.

The specific allergens that trigger reactions may be different in people who develop allergies as adults compared to those who were allergic as children. While kids are most often allergic to eggs, peanuts, and milk, the most common adult-onset allergens are:

• Shellfish (such as crabs, shrimp, scallops, or clams)
• Finned fish (like cod, salmon, or tuna)
• Peanuts
• Tree nuts (such as walnuts, pecans, cashews, or almonds)

Even though these four allergens are the most common among adults, they aren’t the only possible triggers. Researchers have found that adults can develop allergies to all types of food allergens.

What Causes Adult-Onset Food Allergies?

Food allergies occur when your immune system reacts to proteins, known as allergens, in the food that you eat, inhale, or touch. But your immune system doesn’t stay the same your whole life. It changes as you age, and this may cause food allergies to arise that you didn’t have when you were younger. Researchers are still investigating what causes adult-onset food allergies.

Some scientists are trying to find out whether changes in gut bacteria, a family history of food allergies, moving to a different geographic area, or even a delayed diagnosis might be the cause.

It’s also possible that people may develop oral allergy syndrome (OAS) later in life rather than a specific food allergy. OAS is caused by a pollen allergy, and it occurs when you eat fruits or vegetables that contain proteins that resemble those found in pollen. This can cause your body to react as if you were exposed to the pollen allergen. It’s also called cross-reactivity.

OAS is more common among adults than it is in children. It’s especially common in people who already have seasonal allergies.

Symptoms of Adult-Onset Food Allergies

Researchers have found that food allergy symptoms tend to be more severe among those who were diagnosed with a food allergy later in life. Symptoms may include:

• Swelling in the tongue, lips, throat, and face
• Itching or tingling in your mouth
• Hives, itchiness, or other skin reactions
• Diarrhea, abdominal pain, nausea, or vomiting
• Dizziness, fainting, or lightheadedness
• Nasal congestion, wheezing, or difficulty breathing

"I have recently developed an adult allergy to corn, wheat, nuts, and fruits,” one MyFoodAllergyTeam member said. “All the things I loved to eat growing up are now a no-no. My tongue swells so badly I can't talk, and my body is so itchy I scratch my skin open."

In severe cases, a food allergy can trigger a serious, life-threatening reaction called anaphylaxis. Anaphylaxis may cause the food allergy symptoms listed above, as well as a rapid heart rate, weakness, low blood pressure, and unconsciousness.

Next Steps for People With Adult-Onset Food Allergies

If you think you may have experienced an allergic reaction from food as an adult, you should contact an allergist as soon as possible. They can perform allergy testing to determine which allergens may be affecting you.

They can also guide you to treatments that might help you control your symptoms. Your best bet is to avoid the allergens that your provider has identified. Also, start reading food labels in depth so you don’t accidentally eat or drink something that triggers your symptoms.

Your allergist will also prescribe emergency food allergy medications, such as an epinephrine auto-injector. If you’re accidentally exposed to one of your allergens and have a severe allergic reaction, you’ll want to use these medications immediately before calling 911 for emergency medical care.

If you have OAS associated with a pollen allergy, consider asking your allergy specialist about allergy shots (also called immunotherapy). This treatment is administered over the course of several years. It gets your body accustomed to tolerating the allergens that trigger your symptoms. These treatments might not work for everyone with allergies, so it’s a good idea to talk to your allergist to get advice that’s right for you.

Talk With Others Who Understand

MyFoodAllergyTeam is the social network for people with food allergies and their loved ones. On MyFoodAllergyTeam, more than 41,000 members come together to ask questions, give advice, and share their stories with others who understand life with allergies to food.

Did you develop food allergies later in life? How did you discover your allergy? Share your experience in the comments below, or start a conversation by posting on your Activities page.