Food Allergies

Food allergies occur most often in babies and children, but can appear at any age.  Foods that you have eaten for years without problems can cause allergies.

An allergy occurs when something causes your body’s natural defenses to overact.  Some 40-50 million Americans have an allergy of some kind, but food allergies are rare. Up to 4 percent of adults have food allergies.

Here are some answers to common questions about food allergies.


In some people, an allergy can start within minutes of eating a food.  In others, the reaction may not start for several hours. Reactions can be mild, such as a runny nose and sneezing, or very severe, such as swelling of the throat or tongue, wheezing, or a drop in blood pressure.

The most common symptoms of food allergies are:

  • Skin rashes: hives (itchy, red blotches on the skin) and eczema (an itchy, oozy, rash)
  • Intestinal problems: vomiting, nausea, stomach cramps, indigestion and diarrhea

Other common symptoms are:

  • Itchy, stuffy, runny nose and sneezing
  • Swelling of the tongue, lips or throat
  • Asthma (difficulty in breathing), with cough or wheezing
  • Rarely, a severe allergic reaction (anaphylaxis) can be life threatening

Sometimes bad reactions to foods are not caused by an allergy.  Eight percent of children under age six have bad reactions to the foods they eat, but only 2-5 percent actually have a food allergy.  Some people have bad reactions to cow’s milk that are not allergies.  These reactions are sometimes mistaken for a food allergy.  An allergist can find out if your reaction is caused by a food allergy. 


The body’s natural defense network is called the immune system.  It keeps you healthy by fighting off infections and other dangers to good health.  Most people have no problem eating many kinds of foods. An allergic reaction occurs when the immune system attacks a specific food or something in a food by mistake.  This battle causes:

  • Blood vessels to swell up
  • Smooth muscles to contract
  • Skin areas to become red, itchy and swollen


If both your parents have allergies, you have about a 75 percent chance of being allergic.  If one of your parents is allergic, or if one of your relatives from either side has allergies, you have a 30-40 percent chance of having some form of allergy yourself.  If neither parent has allergies, the chance is only 10-15 percent.

The amount or kind of food you eat – and how often you eat it -  may be an important factor in developing a food allergy.


Food AllergiesThe most common foods causing allergies are:

  • Eggs
  • Cow’s milk
  • Peanuts
  • Soy
  • Wheat
  • Tree nuts
  • Fish and shellfish

Almost any food can start an allergy. Foods most likely to cause a severe allergy are peanuts, tree nuts and shellfish.

Someone allergic to a food may also react to related foods. A person allergic to walnuts may also react to pecans. Persons allergic to shrimp may also react to crab and lobster. A person allergic to peanuts may have problems with soy, peas or certain kinds of beans

Most food allergy patients only react to one of two foods. Someone allergic to pecans may not have to stop eating all nuts. This should be discussed with your allergist.


Some people know exactly what food causes their allergy.  They eat peanuts or a product with peanut in it and immediately break out in a rash.  Others need an allergist’s help in finding the cause sometimes, the symptoms show up many hours after they have eaten the food.

Your allergy treatment will typically begin with a complete medical history. Your allergist will ask you about:

  • The symptoms you have after eating the food
  • How long after eating the food these symptoms occur
  • How much of the food you had
  • How often has the reaction occurred
  • What type of medical treatment, if any, you had

The medical history will also include questions about your diet, your family’s medical history, and your home and living area.

Your allergist asks these questions to find out what is causing your allergy or making your symptoms worse. Allergy to pollen in the air, such as ragweed pollen, can be the cause of the swelling or itching in your mouth and throat if you eat certain foods like melons.


Your allergist may recommend allergy tests. This may include skin testing. In an allergy skin test, a very small drop of a liquid food extract, one for each food, is placed on the skin.  The skin is then lightly pricked. This is safe and generally not painful. Within 15 to 20 minutes, a raised bump with redness around it, similar to a mosquito bite, may appear. It shows that you are probably allergic to that food. Sometimes, an allergy blood test may be used. The blood test generally costs more than skin testing.  The results are usually not ready for one to two weeks.

If done right, skin tests or blood tests are reliable and can rule in or out food allergy. Some people do test ‘allergic’ to a food (by skin or blood testing) and yet have no symptoms when they eat that food. To confirm test results, your allergist may ask you to do a challenge test. This means that you have to see if an allergic reaction occurs. This is usually done under an allergist’s supervision.


Your allergist may narrow the search for foods causing allergies by placing you on a special diet. You may be asked to keep a daily food diary. It lists all food you eat and medication you take, along with your symptoms for the day.

If only one or two foods seem to cause allergies, you may try avoiding them. In this diet, you do not eat the suspect food at all for one to two weeks. If the allergic symptoms decrease during that period and flare up when you eat the food again, it is very likely the food is causing your allergy.

However, which food you should avoid (and for how long) and when you should eat the food again (if ever) should be decided together with your allergist. You should never try to eat even a small quantity of any food you and your allergist have decided against.

Your allergist may want to confirm these diet tests with a challenge test.


Once a food allergy is certain, the best treatment is to avoid the food. You need to carefully check ingredient labels of food products. You should learn other names for the food or foods that you and your doctor think it best to avoid to be sure not to eat them.

When you eat out, you should be extra careful. Waiters (and sometimes the kitchen staff) may not always know every dish ingredient on the restaurant’s menu. Sometimes, even walking into a kitchen or an eatery where food is being prepared can cause a dangerous reaction. Vapor may carry extremely small particles that can be harmful.

All patients with food allergies must make some changes in the foods they eat. Your allergist can direct you to helpful resources, such as:

  • Special food allergy cookbooks
  • Patient support groups
  • Registered dietitians


Food AllergiesYou need to have a clear plan of action in case you eat a food you shouldn’t. Place a list of symptoms and your allergist’s instructions for treatment within easy reach in your kitchen. Medications can be very useful in treating many early symptoms of mild food allergies.

If you have had severe allergic reactions, you need to know when and how to give yourself a shot of epinephrine (adrenaline) to treat a severe reaction. You should go to the hospital or call 9-1-1 and arrange for follow-up care when the reaction is severe. Bracelets or necklaces may be worn to quickly alert medical personnel or other caretakers about food allergies.


Over time, allergies to cow’s milk, eggs and soy may disappear. Allergies to peanuts, tree nuts, fish and shellfish typically last a lifetime. About one-third of children and adults who had food allergies at some point are eventually free from food allergies after very carefully avoiding the foods.

After you have avoided foods causing allergies for at least six months, your allergist may want to run a test, under observation, to see if you are cured. If you have no reaction and can eat a normal portion of the food, you will be able to start eating the food again if you wish. If any allergy symptoms occur, you should continue to avoid the foods.

Once you have had a severe, sudden, life-threatening reaction to a certain food you may be advised to never again eat this food. In some very allergic persons, a very small quantity of a food can produce a life-threatening reaction.

By using caution and carefully following an allergist’s advice, you can bring food allergy under control. Please contact your allergist with further questions and concerns about food allergy.


Information provided by ACAAI (American College of Allergy, Asthma & Immunology)

Medical Disclaimer: The information contained on the Chicagoland Allergy web site is presented for the purpose of educating people about allergic conditions. Nothing contained on this web site should be construed nor is intended to be used for medical diagnosis or treatment. It should not be used in place of the advice of your physician or other qualified health care provider.