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 5, and about 3 to 4 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.
The majority of food allergies are triggered by certain proteins in:
- Shellfish, such as shrimp, lobster and crab
- Tree nuts, such as walnuts and pecans
In children, food allergies are commonly triggered by proteins in:
- Tree nuts
Chocolate, long thought by some parents to cause food allergies in children, rarely triggers a food allergy.
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. Food allergies can occur even the first time you eat a food.
The most common food allergy symptoms include:
- Tingling or itching in the mouth
- Hives, itching or eczema
- Swelling of the lips, face, tongue and throat, or other parts of the body
- Wheezing, nasal congestion or trouble breathing
- Abdominal pain, diarrhea, nausea or vomiting
- Dizziness, lightheadedness or fainting
AnaphylaxisIn some people, a food allergy can trigger a severe allergic reaction called anaphylaxis. This can cause life-threatening symptoms, including:
- Constriction and tightening of airways
- A swollen throat or the sensation of a lump in your throat that makes it difficult to breathe
- Shock, with a severe drop in blood pressure
- Rapid pulse
- Dizziness, lightheadedness or loss of consciousness
Emergency treatment is critical for anaphylaxis. Untreated, anaphylaxis can cause a coma or death.
Exercise-induced food allergy
Some people have an allergic reaction to a food triggered by exercise. Eating certain foods may cause you to feel itchy and lightheaded soon after you start exercising. In serious cases, an exercise-induced food allergy can cause reactions such as hives or anaphylaxis. Not eating for a couple of hours before exercising and avoiding certain foods may help prevent this problem.
Pollen-food allergy syndrome
In many people who have hay fever, fresh fruits and vegetables and certain nuts and spices can trigger an allergic reaction that causes the mouth to tingle or itch. In some people, pollen-food allergy syndrome — sometimes called oral allergy syndrome — can cause swelling of the throat or even anaphylaxis. This is an example of cross-reactivity. Proteins in fruits and vegetables cause the reaction because they’re similar to those allergy-causing proteins found in certain pollens. For example, if you’re allergic to ragweed, you may also react to melons; if you’re allergic to birch pollen, you may also react to apples. Cooking fruits and vegetables can help you avoid this reaction. Most cooked fruits and vegetables generally don’t cause cross-reactive oral allergy symptoms.
Common cross-reactivity between pollens and fruits and vegetables:
|If you are allergic to:||Birch pollen||Ragweed pollen||Grasses||Mugwort pollen|
|You may also have a reaction to:||Apples
(cantaloupe, honeydew and watermelon) Tomatoes
Some spices (caraway seeds, parsley, coriander, anise seeds, fennel seeds)
Tests There’s no standard test used to confirm or rule out a food allergy. Your doctor will consider a number of things before making a diagnosis. The following may help determine if you’re allergic to a food or if your symptoms are caused by something else:
- Description of your symptoms. Be prepared to tell your doctor a history of your symptoms — which foods, and how much, seem to cause problems — and whether you have a family history of food allergies or other allergies.
- Physical examination. A careful exam can identify or exclude other medical problems.
- Food diary. Your doctor may ask you to keep a food diary of your eating habits, symptoms and medications to pinpoint the problem.
- Skin test. A skin prick test can determine your reaction to a particular food. In this test, a small amount of the suspected food is placed on the skin of your forearm or back. Your skin is then pricked with a needle, to allow a tiny amount of the substance beneath your skin surface. 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.
- Elimination diet. You may be asked to eliminate suspect foods for a week or two, and then add the food items back into your diet one at a time. This process can help link symptoms to specific foods. However, this isn’t a foolproof method. Psychological factors as well as physical factors can come into play. For example, if you think you’re sensitive to a food, a response could be triggered that may not be a true allergic one. If you’ve had a serve reaction to a food in the past, this method may not be safe.
- Blood test. A blood test can measure your immune system’s response to particular foods by checking the amount of allergy-type antibodies in your bloodstream, known as immunoglobulin E (IgE) antibodies. For this test, a blood sample taken in your doctor’s office is sent to a medical laboratory, where different foods can be tested. However, these blood tests aren’t always accurate.
- Oral food challenge. During this test, done in the doctor’s office, you’ll be given small, but increasing amounts of the suspect food. If you don’t have a reaction during this test, you may be able to include this food in your diet again.
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 (EpiPen, EpiPen Jr, Twinject). 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:
- Carry it with you at all times. It may be a good idea to keep an extra autoinjector in your car or in your desk at work.
- Always be sure to replace epinephrine before its expiration date, or it may not work properly.
- Be sure you know how to use the autoinjector. Also, make sure the people closest to you know how to administer the drug — if they’re with you in an anaphylactic emergency, they could save your life.
While there’s ongoing research to find better treatments to reduce food allergy symptoms and prevent allergy attacks, there isn’t any proven treatment that can prevent or completely relieve symptoms. Unfortunately allergy shots (immunotherapy), a series of injections used to reduce the effect of other allergies such as hay fever, aren’t effective for treating food allergies. Two treatments that have shown some promise are:
- Anti-IgE therapy. The medication omalizumab (Xolair) interferes with the body’s ability to use IgE. The drug is currently being studied for treatment of allergic asthma and food allergies. However, this treatment is still considered experimental and more research needs to be done on the drug’s long-term safety. It has been associated with a potential increased risk of anaphylaxis.
- Oral immunotherapy. Researchers have been studying the use of oral immunotherapy (OIT) as a treatment for food allergy. Small doses of the food you’re allergic to are swallowed or placed under your tongue (sublingual). The dose of the allergy-provoking food is gradually increased. Initial results look promising, even in people with peanut allergy. But, more research needs to be done to ensure that this treatment is safe.