Food Allergies and Food Intolerance
Which Food Allergies Are Most Common?
In adults, the most common foods allergies include:
peanuts (a legume that is one of the chief foods to cause severe anaphylaxis, a sudden drop in blood pressure that can be fatal if not treated quickly)
tree nuts such as walnuts
shellfish such as shrimp, crayfish, lobster, and crab
In children, the food allergy pattern is somewhat different. The most common food allergens that cause problems in children are eggs, milk, and peanuts. Adults usually do not lose their allergies, but children can sometimes outgrow them. Children are more likely to outgrow allergies to milk, eggs, or soy than allergies to peanuts, fish, or shrimp.
The foods that adults or children react to are those foods they eat often. In Japan, for example, rice allergy is more frequent. In Scandinavia, codfish allergy is more common.
Cross Reactivity Food Allergies
If someone has a life-threatening allergic reaction to a certain food, the doctor will counsel the patient to avoid similar foods that might trigger this reaction. For example, if someone has a history of allergy to shrimp, testing will usually show that the person is not only allergic to shrimp but also to other shellfish like crab, lobster, and crayfish. This is called cross-reactivity.
Another interesting example of cross-reactivity occurs in people who are highly sensitive to ragweed. During ragweed pollination season, these people sometimes find that when they try to eat melons, particularly cantaloupe, they have itching in their mouth and they simply cannot eat the melon. Similarly, people who have severe birch pollen allergy also may react to the peel of apples. This is called the "oral allergy syndrome."
Differential Diagnoses For Food Allergies
A differential diagnosis means distinguishing a food allergy from food intolerance or other illnesses. If a patient goes to the doctor's office and says, "I think I have a food allergy," the doctor has to consider the list of other possibilities that may lead to symptoms that could be confused with a food allergy.
One possibility is the contamination of foods with microorganisms, such as bacteria, and their products, such as toxins. Contaminated meat sometimes mimics a food allergy when it is really a type of food poisoning.