Allergy can be defined as a disease state caused by exposure to a particular chemical to which certain individuals have a heightened sensitivity (hypersensitivity), which has an immunological basis. Foods are not the only substances to which people can be allergic. Bee stings, insect bites, pollen, dander, mold spores, house dust, and drugs can also initiate allergies. For such allergens, the symptoms are identical to those found for food allergies, and many individuals suffer multiple sensitivities from food or other sources.
Food allergens are defined as common food proteins which, in certain individuals, produce substances that induce allergic symptoms and can be life threatening. As in all people, the allergens are ingested, passed through the gut epithelium, and circulate in the blood; however, the immune system of some individuals reacts to these food allergens by manufacturing immunoglobulin E (IgE).
Food allergies occur in 2 to 2.5% of the population. It has been estimated that 1 to 3% of children under the age of 6 years have allergies to foods. The frequency of food allergies is highest in infancy and early childhood, but decreases with age. Childhood allergies to egg and cow’s milk usually disappear, but allergies to nuts, legumes, fish, and shellfish tend to linger throughout life. Prevalence of childhood allergies is related to the gastrointestinal epithelial membrane barrier, which is immature during infancy. Thus, the barrier allows more proteins into the circulation, which can sensitize infants to ingested allergens. The mucosal barrier becomes less absorptive and more efficient for digestion as the child matures, and cow’s milk and eggs become less offending. Genetic influence is very strong for food induced allergies. If one parent is allergic, then the risk of the same allergy occurring in offspring is increased by 50%. If both parents show food allergies, the chance of offspring having similar problems increases to 67 to 100%.