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.
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
When to see a doctor
See a doctor or allergist if you have food allergy symptoms shortly after eating. If possible, see your doctor when the allergic reaction is occurring. This will help your doctor make a diagnosis.
Seek emergency treatment if you develop any signs or symptoms of anaphylaxis, such as:
Constriction of airways that makes it difficult to breathe
Shock, with a severe drop in blood pressure
Dizziness or lightheadedness
When you have a food allergy, your immune system mistakenly identifies a specific food or a substance in food as something harmful. Your immune system triggers cells to release antibodies known as immunoglobulin E (IgE) antibodies to neutralize the culprit food or food substance (the allergen). The next time you eat even the smallest amount of that food, the 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 a range of allergy signs and symptoms. They are responsible for causing allergic responses that include dripping nose, itchy eyes, dry throat, rashes and hives, nausea, diarrhea, labored breathing, and even anaphylactic shock.
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:
Chocolate, long thought by some parents to cause food allergies in children, rarely triggers a food allergy.
Food intolerance and other reactions
There are a number of reactions to food that cause similar symptoms to a food allergy. 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. Because a food intolerance may involve some of the same signs and symptoms as a food allergy does — such as nausea, vomiting, cramping and diarrhea — people may confuse the two.
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.
Treatment & Drugs
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.
Lifestyle & Home Remedies
One of the keys to preventing an allergic reaction is to completely avoid the food that causes your symptoms.
Don't assume. Always read food labels to make sure they don't contain an ingredient you're allergic to. Even if you think you know what's in a food, check the label. Ingredients sometimes change. Food labels are required to clearly list whether they contain any common food allergens. Read food labels carefully to avoid these top eight sources of food allergens: milk, eggs, peanuts, tree nuts, fish, shellfish, soy and wheat.
When in doubt, say no thanks. At restaurants and social gatherings, you're always taking a risk that you might eat a food you're allergic to. Many people don't understand the seriousness of an allergic food reaction and may not realize that a tiny amount of a food can cause a severe reaction in some people. If you have any suspicion at all that a food may contain something you're allergic to, steer clear.
Involve caregivers. If your child has a food allergy, enlist the help of relatives, baby sitters, teachers and other caregivers. Make sure they understand how important it is for your child to avoid the allergy-causing food and that they know what to do in an emergency. It's also important to let caregivers know what steps they can take to prevent a reaction in the first place, such as careful hand-washing, and cleaning any surfaces that might have come in contact with the allergy-causing food.