Food allergy is an abnormal response to a food triggered by your body’s immune system.
In adults, the foods that most often trigger allergic reactions include fish, shellfish, peanuts, and tree nuts, such as walnuts. Problem foods for children can include eggs, milk, peanuts, tree nuts, soy, and wheat.
In some people, a food allergy can cause severe symptoms or even a life-threatening reaction known as anaphylaxis.
Symptoms of food allergy include:
• Itching or swelling in your mouth
• Vomiting, diarrhea, or abdominal cramps and pain
• Hives or eczema
• Tightening of the throat and trouble breathing
• Drop in blood pressure
Types of Food Allergies
Food allergies are divided into 3 types, depending on symptoms and when they occur:
• IgE-mediated food allergy – the most common type, triggered by the immune system producing an antibody called immunoglobulin E (IgE). Symptoms occur a few seconds or minutes after eating. There’s a greater risk of anaphylaxis with this type of allergy.
• non-IgE-mediated food allergy – these allergic reactions aren’t caused by immunoglobulin E, but by other cells in the immune system. This type of allergy is often difficult to diagnose as symptoms take much longer to develop (up to several hours).
• mixed IgE and non-IgE-mediated food allergies – some people may experience symptoms from both types.
Diagnosis
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 professional 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.
Treatment
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.
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