The most common food allergy triggers are the proteins in cow's milk, eggs, nuts, wheat, soy, fish, and shellfish. If you're allergic to one of these foods, you may start to notice symptoms within a few minutes to a few hours of eating it. (If you're severely allergic, you might have a reaction after simply touching or smelling the food.) First you may find that your lips, mouth, and throat are swollen and itchy. You may also become congested or have trouble breathing or develop a rash. As the food moves into your stomach, you might suffer from nausea, vomiting, cramps, or diarrhea.

Although more than a third of the adults in this country believe they're allergic to a particular food, studies have found that fewer than 2 percent of Americans have true food allergies. When you're allergic to a food, your immune system mistakenly identifies it as an invader and stimulates the release of chemicals, including histamines, that are meant to help your body expel the offending substance. Just as hay fever makes you sneeze when pollen and mold spores invade your sinuses, a food allergy may cause vomiting or diarrhea as your body tries to get the food out of your system as soon as possible. If your immune system isn't the source of the adverse reaction, you probably have a food intolerance. You may lack an enzyme you need to digest the food, or it may contain an additive that you're sensitive to.

Absolutely. In fact, something as benign as a kiss could trigger an allergic reaction. A study reported in the New England Journal of Medicine found that five percent of a group of 379 people allergic to peanuts, tree nuts, and seeds suffered reactions after kissing people who had consumed those foods. The reactions were mostly mild, though one person needed medication to stop wheezing.

You can develop a food allergy at any time, though most adults who get them do so before the age of 30. Once you've become allergic to a food in your adult years, you won't "grow out of it." In fact, it's possible that the more exposure you get to the food, the more sensitized your immune system will become and the likelier you'll be to have a severe reaction at some point. Be especially careful to avoid the food when you go out, and make it a habit to read food labels closely. Learn the different names used in ingredient lists for the food that causes your allergy; for example, milk may be listed in certain products as casein or sodium caseinate.

If you accidentally ingest a food that you're allergic to, monitor your symptoms carefully. In a mild case, you can take antihistamines to reduce swelling and itching. If you're having a more severe or "anaphylactic" reaction, you may start to have symptoms within 5 to 15 minutes, including a red itchy rash, a swollen mouth and throat, light-headedness, shortness of breath, sneezing, cramping, vomiting, or diarrhea. The symptoms may come on very suddenly and can be life-threatening. The sooner you're treated, the greater your chances of survival are. You can usually stop such a reaction with an injection of epinephrine (adrenaline.) For this reason, you should carry the shot with you at all times. It's also a good idea to wear an identification bracelet that describes what to do in case you go into anaphylactic shock and can't inject yourself. Go to the emergency room and get checked out by a physician even if your symptoms start to subside.

If you feel you've had an allergic reaction to a food, even a relatively mild one, you should see your doctor, who may recommend a consultation with an allergist. After taking a detailed medical history, he or she will ask you to describe your symptoms. If they match the typical food-allergy profile, you'll probably have a skin or blood test to determine whether your symptoms are due to an immune reaction. If the skin test produces a rash or the blood test shows that you have antibodies to the food, there's a good chance that you are allergic. If your allergist feels it's warranted, he or she will prescribe an epinephrine injection kit that you should carry in case of a severe reaction, and will teach you how to use it.

If your symptoms don't match the typical profile or if you think that you're allergic to one or more major food groups or to a wide range of foods, your doctor may ask you to keep a food diary in order to identify all possible triggers. Afterward you'll eliminate the suspected foods from your diet for several weeks to see if your symptoms go away, then add them back one at a time to find out which ones may be causing your problem. (This is called an elimination diet.) Giving up dairy or wheat products can leave big nutritional holes in your diet, so work with your doctor or a dietitian to make sure you continue to get the nutrients you need.

Once you've identified the foods that seem to be triggering your symptoms, your doctor can do specific skin or blood tests to see whether your immune system or your digestive system is to blame. If the tests are negative, you're probably suffering from a food intolerance. Even if you're carrying antibodies, they may be left over from an early-childhood allergy. Sometimes an allergist can tell by the number of antibodies whether they represent a current allergy or a previous one. If the results are unclear, your doctor may conduct a "food challenge" in which you're given increasing amounts of a food (often in disguised form) and watched for symptoms. When all other signs are questionable, this test is the only definitive way to find out whether you're truly allergic to a particular food.

The only way to avoid food-allergy symptoms is to avoid the food. Allergy injections or "desensitization" methods are not recommended for food allergies and in fact are considered dangerous.

About 5 percent of babies and young children have food allergies -- usually to dairy products, wheat, or soy -- that they generally outgrow after their first few years. If you think your child has a food allergy, it's a good idea to get it diagnosed by your pediatrician or an allergist before eliminating the food from your child's diet for good. Your allergist can run tests that will determine whether your child is truly allergic and whether you should carry an epinephrine injection kit in case of an anaphylactic reaction. If an allergy isn't causing the symptoms, your child may be lacking an enzyme needed for the digestion of a particular food. If, say, that food is lactose (the sugar in milk,) a common offender, there's a good chance your child won't have to give up dairy products. For a mild to moderate intolerance, you can usually buy lactose-free products or enzyme pills that your child can take when eating regular dairy foods. If these don't work, ask a doctor or dietitian about how you can make sure your child is getting enough calcium.

References

Last updated September 22, 2009
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