Food allergy affects up to 6 to 8 percent of children under the age of three and 2 percent of adults. If you have an unpleasant reaction to something you have eaten, you might wonder if you have a food allergy. One out of three people either believe they have a food allergy or modify their or their family’s diet. Thus, while food allergy is commonly suspected, health care providers diagnose it less frequently than most people believe.

Food allergy is an abnormal response to a food triggered by the body’s immune system. Allergic reactions to food can cause serious illness and, in some cases, death. Therefore, if you have a food allergy, it is extremely important for you to work with your health care provider to find out what foods cause your allergic reaction.

How Food Allergy Works

Sometimes, a reaction to food is not an allergy at all but another type of reaction called “food intolerance.” Food intolerance is more common than food allergy. The immune system does not cause the symptoms of food intolerance, though these symptoms can look and feel like those of a food allergy. Common causes of food intolerance include food poisoning, histamine toxicity, lactose intolerance, food additives (MSG, sulfites), gluten intolerance, and psychological causes.

If your immune system is inclined to form IgE to certain foods, you must be exposed to the food before you can have an allergic reaction.

As this food is digested, it triggers certain cells in your body to produce a food-specific IgE in large amounts. The food-specific IgE is then released and attaches to the surfaces of mast cells. The next time you eat that food, it interacts with food-specific IgE on the surface of the mast cells and triggers the cells to release chemicals such as histamine. Depending upon the tissue in which they are released, these chemicals will cause you to have various symptoms of food allergy.

Food allergens are proteins within the food that enter your bloodstream after the food is digested. From there, they go to target organs, such as your skin or nose, and cause allergic reactions. An allergic reaction to food can take place within a few minutes to an hour. The process of eating and digesting food affects the timing and the location of a reaction.

If you are allergic to a particular food, you may first feel itching in your mouth as you start to eat the food. After the food is digested in your stomach, you may have GI symptoms such as vomiting, diarrhea, or pain. When the food allergens enter and travel through your bloodstream, they may cause your blood pressure to drop. As the allergens reach your skin, they can cause hives or eczema. When the allergens reach your lungs, they may cause asthma.


Several methods are used to diagnose food allergy. These include a complete history, food diaries, food elimination diets, food challenge tests, as well as skin or blood testing for specific food allergies.


Food allergy is treated by avoiding the foods that trigger the reaction. Once you and your health care provider have identified the foods to which you are sensitive, you must remove them from your diet. To do this, you must read the detailed ingredient lists on each food you are considering eating. Many allergy-producing foods such as peanuts, eggs, and milk, appear in foods one normally would not associate them with. Peanuts, for example, are often used as a protein source, and eggs are used in some salad dressings. The FDA requires ingredients in a packaged food to appear on its label. You can avoid most of the things to which you are sensitive if you read food labels carefully and avoid restaurant-prepared foods that might have ingredients to which you are allergic.

If you are highly allergic, even the tiniest amounts of a food allergen (for example, a small portion of a peanut kernel) can prompt an allergic reaction. If you have severe food allergies, you must be prepared to treat unintentional exposure. Even people who know what they are sensitive to occasionally make a mistake. To protect yourself if you have had allergic reactions to a food, you should:

  • Wear a medical alert bracelet or necklace stating that you have a food allergy and are subject to severe reactions
  • Carry a syringe of adrenaline (epinephrine), obtained by prescription from your health care provider, and be prepared to give it to yourself if you think you are getting a food allergic reaction
  • Seek medical help immediately by either calling the rescue squad or by getting transported to an emergency room

Anaphylactic allergic reactions can be fatal even when they start off with mild symptoms such as a tingling in the mouth and throat or GI discomfort. Schools and day care centers must have plans in place to address any food allergy emergency. Parents and caregivers should take special care with children and learn how to:

  • Protect children from foods to which they are allergic
  • Manage children if they eat a food to which they are allergic
  • Give children epinephrine

There are several medicines that you can take to relieve food allergy symptoms that are not part of an anaphylactic reaction. These include:

  • Antihistamines to relieve GI symptoms, hives, or sneezing and a runny nose
  • Bronchodilators to relieve asthma symptoms

You should take these medicines if you have accidentally eaten a food to which you are allergic. They do not prevent an allergic reaction when taken before eating the food. No medicine in any form will reliably prevent an allergic reaction to that food before eating it.

Food Allergy in Infants and Children

Allergy to cow’s milk is particularly common in infants and young children. In addition to causing hives and asthma, it can lead to colic and sleeplessness, and perhaps blood in the stool or poor growth. Infants are thought to be particularly susceptible to this allergic syndrome because their immune and digestive systems are immature. Milk allergy can
develop within days to months of birth. If your baby is on cow’s milk formula, your provider may suggest a change to soy formula or an elemental formula if possible. Elemental formulas are produced from processed proteins with supplements added. There are few if any allergens within these materials.

Health care providers sometimes prescribe glucocorticosteroid drugs to treat infants with very severe GI reactions to milk formulas. Fortunately, this food allergy tends to go away within the first few years of life. Breast feeding often helps babies avoid feeding problems related to allergic reactions. Therefore, health experts often suggest that mothers feed their baby only breast milk for the first 6 to 12 months of life to avoid milk allergy from developing within that time frame.

Some babies are very sensitive to a certain food. If you are nursing and eat that food, sufficient amounts can enter your breast milk to cause a food reaction in your baby. To keep possible food allergens out of your breast milk, you might try not eating those foods that could cause an allergic reaction in your baby, such as peanuts. There is no conclusive evidence that breast feeding prevents allergies from developing later in your child’s life. It does, however, delay the start of food allergies by delaying your infant’s exposure to those foods that can prompt allergies. Plus, it may avoid altogether food allergy problems sometimes seen in infants.

By delaying the introduction of solid foods until your baby is 6 months old or older, you can also prolong your baby’s allergy-free period. In addition, the American Academy of Pediatrics recommends you delay adding eggs to your child’s diet until he or she is 2 years old and peanuts, tree nuts, and fish until he or she is 3 years old.

This information was adapted from the National Institute of Allergy and Infectious Diseases handouts on airborne allergens and food allergy.

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