What Are Food Allergies?

A food allergy happens when the body's immune system, which normally fights infections, sees the food as an invader. This leads to an allergic reaction. 

Even if previous reactions have been mild, someone with a food allergy is always at risk for the next reaction being life-threatening. So anyone with a food allergy must avoid the problem food(s) entirely and always carry emergency injectable epinephrine.

What Are the Most Common Food Allergens?

People can be allergic to any food, but these cause most food allergy reactions:

• milk
• eggs
• peanuts
• soy
• wheat
• tree nuts (such as walnuts and cashews)
• fish
• shellfish (such as shrimp)
• sesame

What Are the Signs & Symptoms of a Food Allergy?

With a food allergy, the body reacts as though that particular food product is harmful. As a result, the body's immune system (which fights infection and disease) creates antibodies to fight the food .

Every time the person eats (or, in some cases, handles or breathes in) the food, the body releases chemicals like . This triggers allergic symptoms that can include:

• wheezing
• trouble breathing
• coughing
• hoarseness
• throat tightness
• belly pain
• vomiting
• diarrhea
• itchy, watery, or swollen eyes
• hives
• red spots
• swelling
• a drop in blood pressure, causing lightheadedness or loss of consciousness (passing out)

Sometimes, an allergy can cause a severe reaction called anaphylaxis. Anaphylaxis might start with some of the same symptoms as a less severe reaction, but can quickly get worse. The person may have trouble breathing or pass out. More than one part of the body might be involved. If it isn't treated with injectable epinephrine, anaphylaxis can be life-threatening.

What Is a Food Intolerance?

People often confuse food allergies with food intolerance. The symptoms of food intolerance can include burping, indigestion, gas, loose stools, headaches, nervousness, or a feeling of being "flushed." But food intolerance:

• doesn't involve the immune system
• can happen because a person can't digest a substance, such as lactose
• can be unpleasant but is rarely dangerous

How Is a Food Allergy Diagnosed?

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, you'll probably see an . The allergist will ask you questions again and do a physical exam (such as listening to your lungs). They'll 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.

If the test results are unclear, the allergist may do a food challenge:

• During this test, a person slowly gets increasing amounts of the potential food allergen to eat while being watched for symptoms by the doctor. The test must be done in an allergist's office or hospital with access to immediate medical care and medicines because a life-threatening reaction could happen.

Food challenge tests are also done to see if people have outgrown an allergy.

How Are Food Allergies Treated?

There's no cure for food allergies, and the only real way to treat them is to avoid the food in question. But doctors can prescribe medicines to help lessen symptoms if they do happen, and even save a person's life if the reaction is serious.

If you have a food allergy, always have two epinephrine auto-injectors nearby in case of a severe reaction. An epinephrine auto-injector is a prescription medicine that comes in a small, easy-to-carry container. It's easy to use. Your doctor will show you how. Always have two auto injectors nearby in case one doesn't work or you need a second dose.

The doctor can also give you an allergy action plan, which helps you prepare for, recognize, and treat an allergic reaction. Share the plan with anyone else who needs to know, such as relatives, school officials, and coaches. Also consider wearing a medical alert bracelet.

Time matters in an allergic reaction. If you start having serious allergic symptoms, like trouble breathing or throat tightness, use the epinephrine auto-injector right away (or have someone give you the shot). Also use it right away if symptoms involve two different parts of the body, like hives with vomiting. Then call 911 and go to the emergency room. Medical supervision is important because even if the worst seems to have passed, a second wave of serious symptoms can happen.

What Else Should I Know?

If you have food allergies of any kind, you'll become an expert in reading food labels. Makers of foods sold in the United States must state whether foods contain any of the top common allergens.

Label information helps if you're buying packaged foods, but what about when you eat away from home? If you have a food allergy, tell 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.

Coping 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.

You can learn more about managing food allergies online at:

• Food Allergy Research and Education Network (FARE)