Doctors are diagnosing more and more people with food allergies. People can be allergic to any food, but eight common allergens account for most food allergy reactions:
- tree nuts (such as walnuts and cashews)
- shellfish (such as shrimp)
Young kids who have food allergies often outgrow their allergy — but not always. A lot depends on which foods someone is allergic to. Some foods are easier to outgrow than others. For example, most kids who are allergic to milk, eggs, wheat, or soy outgrow their allergies by the time they're 5 years old. But only about 20% of people with peanut allergy and about 10% of kids with tree nut allergy outgrow their allergy. Fish and shellfish allergies usually develop later in life, and people are unlikely to outgrow them.
What Happens in the Body
Food allergies happen when someone's immune system mistakenly believes that something the person ate is harmful to the body. In an attempt to "protect" the body, the immune system produces IgE antibodies to that food. IgE antibodies then trigger mast cells (which are allergy cells in the body) to release chemicals into the bloodstream.
One of these chemicals is histamine (pronounced: HISS-tuh-meen). Histamine acts on the eyes, nose, throat, lungs, skin, or gastrointestinal tract and causes symptoms of the allergic reaction.
Once the body has made antibodies against a certain food, those antibodies instantly recognize that food. Each time the person eats the food, the body releases histamine into the bloodstream again, creating allergy symptoms. In severe food allergies, reactions can occur even if the person touches or breathes in particles of the food.
Some reactions can be very mild and involve only one system of the body, like hives on the skin. Other reactions can be more severe and involve more than one part of the body. Most reactions last less than a day and affect any of these four body systems:
- Skin. Skin reactions are the most common type of food allergy reactions. They can take the form of itchy, red, bumpy rashes (hives), eczema, or redness and swelling around the mouth or face.
- Gastrointestinal system. Symptoms can take the form of belly cramps, nausea, vomiting, or diarrhea.
- Respiratory system. Symptoms can range from a runny or stuffy nose, itchy, watery eyes, and sneezing to the triggering of asthma with coughing and wheezing.
- Cardiovascular system. A person may feel lightheaded or faint.
Most reactions happen pretty soon after eating a particular food. Everyone's different, though. So although two people may have peanut allergy, for example, both may not have the same type of allergic reaction. And even the same person can have different reactions to a particular food, depending on factors like how much he or she was exposed to.
When someone has a serious allergic reaction that involves two or more body systems, this condition is known as anaphylaxis. This is a sudden, potentially life-threatening allergic reaction. In addition to the symptoms mentioned above, anaphylaxis can cause swelling of the airway, serious breathing difficulty, a drop in blood pressure, loss of consciousness, and, in some cases, even death.
Because food allergies can be severe, people who think they might be allergic to a certain food should see a doctor. It may be tempting to just not eat that food, but allergens can be hidden in surprising places, and without a doctor's diagnosis a person can't know exactly what to avoid.
What Do Doctors Do?
Your doctor will look for any other conditions that could be causing symptoms. For example, if you have diarrhea after drinking milk, the doctor may check to see if lactose intolerance could be causing the problem instead of a food allergy. Another condition that may mimic food allergy symptoms is celiac disease. People with celiac disease are not able to tolerate gluten, a protein found in wheat and certain other grains.
If your doctor thinks you have a food allergy, he or she will probably refer you to an allergist. The allergist will ask you questions again and perform a physical exam (such as listening to your lungs). He or she will probably also run some tests to help diagnose the problem.
The most common kind of allergy test is a skin test. A doctor or nurse will scratch the skin (usually on the forearm or back) with a tiny bit of the extract, then wait a few minutes to see if there's a reaction. Doctors may also do other tests, including a blood test. Blood tests show if there are antibodies to a particular food in the person's blood — indicating an immune system reaction to that food.
If you've found out that you have a food allergy, your allergist will work with you to create a treatment plan that is tailored to your particular needs. You should also work together to develop a written food allergy emergency action plan to keep at school to help you avoid a serious reaction — and to provide guidance in case you do have a reaction.
There's no cure for food allergies, and the only real way to treat them is to avoid the food in question. Fortunately, doctors can prescribe medications to help lessen symptoms if they do happen — and even save a person's life if the reaction is serious.
Medications for Treating Food Allergies
Antihistamines can treat isolated symptoms such as hives, runny nose, or abdominal pain associated with an allergic reaction.
Breathing difficulties such as allergy-triggered asthma can be a sign that something serious is going on, though. If your doctor diagnoses you with severe allergies, he or she may prescribe a medication called epinephrine, which can be lifesaving if a person has anaphylaxis. Because it's important that the medication get into a person's bloodstream quickly, epinephrine comes in an auto-injector.
If your doctor has prescribed epinephrine, you'll need to take the auto-injector with you everywhere you go and also keep one on hand at home, school, and any relatives' or friends' homes that you visit a lot.
So how do you know when you should use epinephrine? Your doctor will go over this with you, but signs and symptoms of anaphylaxis include:
- a sensation of tightness in the throat
- difficulty breathing
- any symptoms in two or more of the body systems above (skin, gastrointestinal, respiratory, and cardiovascular systems), such as hives combined with abdominal pain, or tingling lips combined with difficulty breathing
If you have to give yourself a shot of epinephrine (or someone else gives it to you), call 911 immediately afterward so an ambulance can take you to the hospital. This is important because sometimes there can be a second wave of symptoms. Medical staff need to watch anyone who has used epinephrine for a severe allergy in case the person needs additional treatment.
Avoiding Food Allergens
If you have food allergies of any kind, you'll become an expert in reading food labels.
Makers of packaged foods sold in the United States must list on their labels whether the product contains milk, eggs, fish, shellfish, tree nuts, peanuts, wheat, or soy. This information should appear in or near the list of ingredients. This helps a person know if the "hydrolyzed vegetable protein" in a food comes from peanuts, for example. It also helps avoid a lot of confusion, such as needing to know that the ingredient "albumin" comes from eggs.
Label information helps if you're buying packaged foods, but what about restaurants, coffee shops, ice cream parlors, and other eateries? If you have a food allergy, you'll need to let the people serving you know about it. Most of the time, you can't stop there: Ask what each food on a menu or in the display case contains. If the people helping you don't know, see if they can find out (from the chef or person who prepared the food).
You'll also need to be aware of other food pitfalls, such as the possibility that the food you're allergic to could get into other items from cutting surfaces, shared utensils, etc.
Living with a food allergy can be hard. If you know someone with food allergy, show your support and understanding — some people with food allergies may feel left out or awkward. And if you have a food allergy, let your friends know. Chances are, they'll understand and look out for you.
Reviewed by: Sheelagh M. Stewart, RN, MPH
Date reviewed: November 2011