Food allergy is an immune system reaction that occurs soon after eating a certain food. Even a tiny amount of the allergy-causing food can trigger signs and symptoms such as digestive problems, hives or swollen airways. In some people, a food allergy can cause severe symptoms or even a life-threatening reaction known as anaphylaxis.
Food allergy affects an estimated 6 to 8 percent of children under age 3 and up to 3 percent of adults. While there's no cure, some children outgrow their food allergy as they get older.
It's easy to confuse a food allergy with a much more common reaction known as food intolerance. While bothersome, food intolerance is a less serious condition that does not involve the immune system.
For some people, an allergic reaction to a particular food may be uncomfortable but not severe. For other people, an allergic food reaction can be frightening and even life-threatening. Food allergy symptoms usually develop within a few minutes to two hours after eating the offending food.
The most common food allergy signs and symptoms include:
In some people, a food allergy can trigger a severe allergic reaction called anaphylaxis. This can cause life-threatening signs and symptoms, including:
Emergency treatment is critical for anaphylaxis. Untreated, anaphylaxis can cause a coma or even death.
When you have a food allergy, your immune system mistakenly identifies a specific food or a substance in food as something harmful. In respose, your immune system triggers cells to release an antibody known as immunoglobulin E (IgE) to neutralize the
allergy-causing food or food substance (the allergen).
The next time you eat even the smallest amount of that food, IgE antibodies sense it and signal your immune system to release a chemical called histamine, as well as other chemicals, into your bloodstream. These chemicals cause allergy symptoms.
In adults, the majority of food allergies are triggered by certain proteins in:
In children, food allergies are commonly triggered by proteins in:
Pollen-food allergy syndrome
Also known as oral allergy syndrome, pollen-food allergy syndrome affects many people who have hay fever. In this condition, certain fresh fruits and vegetables or nuts and spices can trigger an allergic reaction that causes the mouth to tingle or itch. In serious cases, the reaction results in swelling of the throat or even anaphylaxis.
Proteins in certain fruits, vegetables, nuts and spices cause the reaction because they're similar to allergy-causing proteins found in certain pollens. This is an example of cross-reactivity.
When you cook foods that trigger pollen-food allergy syndrome, your symptoms may be less severe.
This following table shows the specific fruits, vegetables, nuts and spices that can cause pollen-food allergy syndrome in people who are allergic to different pollens.
Exercise-induced food allergy
Eating certain foods may cause some people to feel itchy and lightheaded soon after starting to exercise. Serious cases may even involve hives or anaphylaxis. Not eating for a couple of hours before exercising and avoiding certain foods may help prevent this problem.
Food intolerance and other reactions
A food intolerance or a reaction to another substance you ate may cause the same signs and symptoms as a food allergy does — such as nausea, vomiting, cramping and diarrhea.
Depending on the type of food intolerance you have, you may be able to eat small amounts of problem foods without a reaction. By contrast, if you have a true food allergy, even a tiny amount of food may trigger an allergic reaction.
One of the tricky aspects of diagnosing food intolerance is that some people are sensitive not to the food itself but to a substance or ingredient used in the preparation of the food.
Common conditions that can cause symptoms mistaken for a food allergy include:
This chronic digestive condition is triggered by eating gluten, a protein found in bread, pasta, cookies, and many other foods containing wheat, barley or rye.
If you have celiac disease and eat foods containing gluten, an immune reaction occurs that causes damage to the surface of your small intestine, leading to an inability to absorb certain nutrients.
Food allergy risk factors include:
Fortunately, children typically outgrow allergies to milk, soy, wheat and eggs. Severe allergies and allergies to nuts and shellfish are more likely to be lifelong.
Factors that may increase your risk of developing an anaphylactic reaction include:
Complications of food allergy can include:
The best way to prevent an allergic reaction is to know and avoid foods that cause signs and symptoms. For some people, this is a mere inconvenience, but others find it a greater hardship. Also, some foods — when used as ingredients in certain dishes — may be well-hidden. This is especially true in restaurants and in other social settings.
If you know you have a food allergy, follow these steps:
Don't be reluctant to make your needs known. Restaurant staff members are usually more than happy to help when they clearly understand your request.
If your child has a food allergy, take these precautions to ensure his or her safety:
There's no perfect test used to confirm or rule out a food allergy. Your doctor will consider a number of factors before making a diagnosis. These factors include.
If you're allergic to a particular substance being tested, you develop a raised bump or reaction. Keep in mind, a positive reaction to this test alone isn't enough to confirm a food allergy.
For this test, a blood sample taken in your doctor's office is sent to a medical laboratory, where different foods can be tested.
An elimination diet can't tell you whether your reaction to a food is a true allergy instead of a food sensitivity. Also, if you've had a severe reaction to a food in the past, an elimination diet may not be safe.
The only way to avoid an allergic reaction is to avoid the foods that cause signs and symptoms. However, despite your best efforts, you may come into contact with a food that causes a reaction.
For a minor allergic reaction, over-the-counter or prescribed antihistamines may help reduce symptoms. These drugs can be taken after exposure to an allergy-causing food to help relieve itching or hives. However, antihistamines can't treat a severe allergic reaction.
For a severe allergic reaction, you may need an emergency injection of epinephrine and a trip to the emergency room. Many people with allergies carry an epinephrine autoinjector (Adrenaclick, EpiPen). This device is a combined syringe and concealed needle that injects a single dose of medication when pressed against your thigh.
If your doctor has prescribed an epinephrine autoinjector: