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 8% of children under age 5 and up to 4% of adults. While there's no cure, some children outgrow their food allergies 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.

SYMPTOMS

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 2 hours after eating the offending food. Rarely, symptoms may be delayed for several hours.

The most common food allergy signs and 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

Anaphylaxis

In some people, a food allergy can trigger a severe allergic reaction called anaphylaxis. This can cause life-threatening signs and symptoms, including:

Constriction and tightening of the 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 even death.

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:

Your symptoms - Give your doctor a detailed history of your symptoms — which foods, and how much, seem to cause problems.

Your family history of allergies - Also share information about members of your family who have allergies of any kind.

A physical examination - A careful exam can often identify or exclude other medical problems.

A 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. A doctor or another health care provider then pricks your skin 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.

A blood test - A blood test can measure your immune system's response to particular foods by measuring the allergy-related antibody known as immunoglobulin E (IgE).

For this test, a blood sample taken in your doctor's office is sent to a medical laboratory, where different foods can be tested.

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, elimination diets aren't foolproof.

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.

Oral food challenge - During this test, done in the doctor's office, you'll be given small but increasing amounts of the food suspected of causing your symptoms. 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.

For a minor allergic reaction, prescribed antihistamines or those available without a prescription may help reduce symptoms. These drugs can be taken after exposure to an allergy-causing food to help relieve itching or hives.

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. This device is a combined syringe and concealed needle that injects a single dose of medication when pressed against your thigh.

Experimental treatments

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.

One treatment currently being studied as a treatment for food allergy is oral immunotherapy. In this treatment, 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.

Lifestyle and home remedies

Don't assume. Always read food labels to make sure they don't contain an ingredient you're allergic to.

Food labels are required to clearly list whether the food products contain any common food allergens. Read food labels carefully to avoid the most common 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.

Involve caregivers. If your child has a food allergy, enlist the help of relatives, babysitters, teachers and other caregivers. Make sure that 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.