Food allergies occur when the body's immune system overreacts to substances in food you have eaten, triggering an allergic reaction. food allergies are more common in young children than in adults. This may be because children's immune and digestive systems are not completely developed.²

• Eggs, milk, peanuts, wheat, soy, and fish cause most of the allergic reactions in children. Some babies are so sensitive to these foods that if the offending food is eaten by the mother, drinking her breast milk can cause a reaction. Most children outgrow allergies to milk, wheat, eggs, and soy between ages 3 and 5. Children rarely outgrow an allergy to peanuts or fish.
• Peanuts, tree nuts (such as walnuts or almonds), fish, and shellfish cause most of the allergic reactions in teens and adults. Adults generally remain allergic to the food for life.

food allergies are most common in people who are atopic, meaning they have an inherited tendency to develop allergic conditions. These people are more likely to have asthma, various allergies, and a skin condition called atopic dermatitis.

If you are highly sensitive to a particular food, you may have an allergic reaction by simply being near the food. Flying in airplanes where other passengers are eating peanuts or simply eating in a seafood restaurant may cause symptoms.

The more common a food is, the more likely it is that people will be allergic to it. For example, rice allergy is seen in Japan, and codfish allergy is seen in Scandinavia. As foods from around the world have become more available, the number of allergic reactions to exotic fruits such as kiwi and papaya and to seeds such as sesame seeds and poppy seeds have increased.

Because peanuts are used in so many foods, peanut allergy has increased in the United States in the past two decades and is now a major cause of severe allergic food reactions. Peanut allergy is usually lifelong and tends to become more severe over time. For more information, see the topic peanut allergy.

Celiac disease is caused by an allergy to a protein (gluten) found in wheat and some other grains. For more information, see the topic Celiac Disease.

Cross-reactivity

Many people are allergic to foods that are similar or somehow related. This is called cross-reactivity. For example, if you are allergic to shrimp, you may also be allergic to other shellfish, like crab or lobster. If you are allergic to peanuts, you may be allergic to other members of the legume family, such as peas and beans.

Oral allergy syndrome is a type of cross-reactivity. In this syndrome, people who have pollen allergies (such as a grass allergy) may develop itching, redness, and swelling of the lips and mouth when they eat fruits or vegetables that contain a protein that reacts with the pollen. These symptoms usually resolve quickly and do not involve other body parts.