For someone with a food allergy, eating the problem food triggers an abnormal response from the body's immune system.
The most common foods that cause an allergic reaction in adults are milk, eggs, peanuts, tree nuts, fish, shellfish, fruits, and soy and wheat products. Children with a food allergy tend to react to peanuts, tree nuts,eggs, milk, wheat, soy, or fish.
Although many people believe they have a food allergy, true food allergies are not that common. Approximately 5 percent of children under 5 years of age are affected by food allergy. Of all teenagers and adults, 4 percent are allergic to foods.
A food intolerance is much more common and refers to a metabolic disorder that doesn't involve the immune system. A person with lactose intolerance, for instance, doesn't produce enough of the enzyme needed to digest milk sugar. Eating milk products may cause bloating, diarrhea, or cramping.
A food allergy causes a reaction when only a tiny amount of the problem food is eaten. For a person with a food intolerance, the symptoms become worse as more of the food is eaten.
Other types of food intolerance involve reactions to food additives, such as dyes, flavorings, and preservatives. Certain diseases can cause symptoms that mimic a food allergy. These include ulcers, cancers of the gastrointestinal tract, and celiac disease. Foods contaminated with microorganisms, such as bacteria, and their toxins can produce symptoms that appear to be a reaction to food. Natural substances, such as histamine, can occur in foods, such as cheese and wine, and these stimulate a reaction similar to an allergic reaction.
These are possible symptoms of a food allergy:
Hives and swelling
Eczema (itchy, scaly, and red skin)
Stuffy nose, sneezing, itchy eyes, and watering eyes
These severe symptoms are a medical emergency (call 911):
Coughing, wheezing, hoarseness, lump in throat, or trouble breathing
Abdominal cramps, diarrhea, vomiting
Swelling of the tongue or throat
Tingling of hands, feet, or scalp
Tongue or throat swelling can be life-threatening because it may block the airways. Some people also may be subject to a sudden systemic reaction called anaphylaxis, which is rare but potentially fatal. Anaphylaxis is most commonly associated with eating nuts, peanuts, and shellfish.
People who are allergic to a certain food are also likely to be allergic to other similar foods. If you are allergic to shrimp, for instance, you should also avoid eating crab, lobster, and crayfish. This "cross-reactivity" also may occur between different types of allergies. A person who is allergic to ragweed may develop allergy symptoms when eating melons during ragweed season. Likewise, a person allergic to birch pollen may also develop allergy symptoms when eating an apple peel.
Dealing with an allergy
Take these steps to keep adverse reactions to food from ruling your life:
Visit your doctor. To diagnose a food allergy, your health care provider will take a detailed history that will include the type of symptoms, when they occurred, and foods eaten before symptoms occurred.
Keep a food diary. Keep a record of each time you have an adverse reaction, including the date and time, type and severity of symptoms, and what you remember doing and eating in the previous six hours. Review the diary with your doctor.
Avoid foods that trigger your allergy once they are identified. Learn the various names of the foods to which you are allergic so you can identify them on food labels. For example, milk products can be called caseinates, eggs can be called albumin, peanuts can be called ground nuts. No medications exist to cure a food allergy. In some cases, if you avoid an offending food for long enough--perhaps for several years--your body may lose its sensitivity to it.
Let people know you have a food allergy. Friends, family, and others who may be serving you food need to know about your allergy. Ask about the menu before ordering foods in restaurants if you think they might contain foods to which you are allergic.
Be prepared for emergencies. If you or your child is at risk for a life-threatening allergic reaction, ask your doctor how to respond in case of emergency. Explain to family members or school staff how to recognize and deal with severe reactions. If prescribed, carry a supply of epinephrine to reverse anaphylaxis at all times. Teach yourself and others how to use it.
More about anaphylaxis
Anaphylaxis can occur within minutes to two hours after eating the problem food. Symptoms can range from mild to life-threatening. The reaction may begin with a tingling sensation, itching or metallic taste in the mouth. Symptoms can then become progressively worse, sometimes taking only minutes to advance. In others, symptoms may occur, ease and then return two to three hours later. This is called a biphasic reaction.
Any anaphylactic reaction should be treated as a medical emergency. Epinephrine is given as treatment because it helps prevent the progression of symptoms. Epinephrine is available by prescription. If you have been prescribed this medication, you must carry it with you at all times. Antihistamines and steroids also may be given as treatment, but never instead of epinephrine because these medications don't reverse the symptoms of anaphylaxis.