What Are Food Allergies?

Milk, eggs, soy, wheat, tree nuts, peanuts, fish, and shellfish are among the most common foods that cause allergies.

Food allergies can cause serious and even deadly reactions. So it's important to know how to recognize an allergic reaction and to be prepared if one happens.

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 allergen .

Every time the person eats (or, in some cases, handles or breathes in) the food, the body releases chemicals like histamine . This triggers allergic symptoms that can affect the respiratory system, gastrointestinal tract, skin, or cardiovascular system.

Symptoms 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)

People often confuse food allergies with food intolerance because of similar symptoms. 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

What Are the Most Common Food Allergens?

A child could be allergic to any food, but these eight common allergens account for 90% of all reactions in kids:

  1. milk
  2. eggs
  3. peanuts
  4. soy
  5. wheat
  6. tree nuts (such as walnuts and cashews)
  7. fish
  8. shellfish (such as shrimp)

In general, most kids with food allergies outgrow them. Of those who are allergic to milk, about 80% will eventually outgrow the allergy. About two-thirds with allergies to eggs and about 80% with a wheat or soy allergy will outgrow those by the time they're 5 years old. Other food allergies may be harder to outgrow.

What Happens in a Food Allergy Reaction?

Food allergy reactions can vary from person to person. Sometimes the same person can react differently at different times. So it's very important to quickly identify and treat food allergy reactions.

Reactions can:

  • be very mild and only involve one part of the body, like hives on the skin
  • be more severe and involve more than one part of the body
  • happen within a few minutes or up to 2 hours after contact with the food

Food allergy reactions can affect any of these four areas of the body:

  1. skin: itchy red bumps (hives); eczema; redness and swelling of the face or extremities; itching and swelling of the lips, tongue, or mouth (skin reactions are the most common type of reaction)
  2. gastrointestinal tract: belly pain, nausea, vomiting, or diarrhea
  3. respiratory system: runny or stuffy nose, sneezing, coughing, wheezing, shortness of breath
  4. cardiovascular system: lightheadedness or fainting

Sometimes, an allergy can cause a severe reaction called anaphylaxis, even if a previous reaction was mild. 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, anaphylaxis can be life-threatening.

How Is a Food Allergy Diagnosed?

If your child might have a food allergy, the doctor will ask about:

  • your child's symptoms
  • how often the reaction happens
  • the time it takes between eating a particular food and the start of symptoms
  • whether any family members have allergies or conditions like eczema and asthma

The doctor will look for any other conditions that could cause the symptoms. For example, if your child seems to have diarrhea after drinking milk, the doctor may check to see if lactose intolerance could be the cause. Celiac disease — a condition in which a person cannot tolerate the protein gluten — also can cause similar symptoms.

The doctor might refer you to an allergist (allergy specialist doctor), who will ask more questions and do a physical exam. The allergist probably will order tests to help make a diagnosis, such as:

  • a skin test. This test involves placing liquid extracts of food allergens on your child's forearm or back, pricking the skin, and waiting to see if reddish raised spots (called wheals) form within 15 minutes. A positive test to a food only shows that your child might be sensitive to that food.
  • blood tests to check the blood for IgE antibodies to specific foods

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.

More often, though, food challenge tests are done to see if people have outgrown an allergy.

How Are Food Allergies Treated?

If your child has a food allergy, the allergist will help you create a treatment plan. Treatment usually means avoiding the allergen and all the foods that contain it.

You'll need to read food labels so you can avoid the allergen. Makers of foods sold in the United States must state whether foods contain any of the top eight most common allergens: milk, eggs, fish, shellfish, tree nuts, peanuts, wheat, or soy.

For more information on foods to avoid, check sites such as the Food Allergy Research and Education network (FARE).

There's no cure for food allergies. But medicines can treat both minor and severe symptoms. Antihistamines might be used to treat symptoms such as hives, runny nose, or belly pain from an allergic reaction.

If your child has any kind of serious food allergy, the doctor will want him or her to carry an epinephrine auto-injector in case of an emergency.

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. Kids who are old enough can be taught how to give themselves the injection. If they carry the epinephrine, it should be nearby, not left in a locker or in the nurse's office.

Allergic Reaction Instruction Sheet

Wherever your child is, caregivers should always know where the epinephrine is, have easy access to it, and know how to give the shot. Staff at your child's school should know about the allergy and have an action plan in place. Your child's medicines should be accessible at all times. Also consider having your child wear a medical alert bracelet.

Signs and symptoms of anaphylaxis that would require epinephrine include:

  • hoarseness
  • throat feels tight
  • swelling in the mouth
  • trouble breathing
  • any symptoms from two or more body systems (skin, heart, lungs, etc.), such as hives and belly pain
  • any other combination of two or more symptoms that affect different parts of the body

Every second counts in an allergic reaction. If your child starts having serious allergic symptoms, give the epinephrine auto-injector right away. Also give it right away if the symptoms involve two different parts of the body, like hives with vomiting. Then call 911 and take your child to the emergency room. Your child needs to be under medical supervision because even if the worst seems to have passed, a second wave of serious symptoms can happen.

It's also a good idea to carry an over-the-counter (OTC) antihistamine for your child, as this can help treat mild allergy symptoms. Use antihistamines after — not as a replacement for — the epinephrine shot during life-threatening reactions.

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