Causes and symptoms
Allergies are caused by the immune system's reaction to a particular food. Usually, a child will have had a prior exposure before IgE or specific histamines are produced.
Food intolerance is often put into the same category as food allergy, even though there may be an entirely different mechanism involved. In these cases, the digestive tract reacts to a specific part of the food; for example, the protein or the sugar in a specific food. The digestive system rebels, resulting in gas, bloating, upset stomach, diarrhea, nausea, or vomiting. Many times, these responses are due to eating food contaminated with bacteria, rather than a true food allergy. In other cases, the child's reaction is due to an underlying digestive disorder such as irritable bowel syndrome, which is a chronic condition that is often triggered by specific types of food.
Gluten intolerance is not an allergy. It is a disease called celiac disease, or gluten-sensitive enteropathy. The body cannot process gluten found in wheat and other grains. Though the immune system is involved, celiac disease does not behave as a true allergy. Its treatment is like many food allergies, namely avoidance of the offending substance, which in this case is gluten.
Some children may lack a specific enzyme needed to metabolize certain foods. About 10 percent of all adults and older children have lactose intolerance. There are two forms of lactose intolerance: inherited and acquired. The inherited form (autosomal recessive) is extremely rare and severe. The acquired type is very common, and occurs in older children (not infants) and adults. It is distressing, but not life-threatening, and occurs with increased frequency in African Americans. Sometimes infants, as well as older children and adults, have a transient lactose deficiency after an episode of diarrhea.
Children with lactose intolerance have a lactase deficiency that keeps them from processing milk and milk products. These children can often drink milk that has had this enzyme introduced into the product. Some children can drink milk that has acidiphilus bacteria put into it. This bacteria breaks down the lactose, or milk sugar, in the milk so that the child can tolerate it. Some children with lactose intolerance cannot drink whole milk, but can eat cheese or drink low-fat buttermilk in small quantities. This is different from a true milk allergy where even a small amount of any dairy product will produce a reaction.
Some children may also be intolerant of food colorings, additives, and preservatives. Among these are yellow dye number 5, which can cause hives; and monosodium glutamate, which produces flushing, headaches, and chest pain. Sulfites, another additive, have been found to cause asthmatic reactions and even anaphylactoid reactions. Sulfites are preservatives used in wines, maraschino cherries, seafood, and soft drinks. They are sometimes put on fresh fruits and lettuce to maintain their fresh appearance, on red meats to prevent brown discoloration, and even in prepared deli foods like crab salad. Sulfites appear on food labels as sodium sulfite, sodium bisulfite, potassium bisulfite, sulfur dioxide, and potassium metabisulfite. The U.S. Food and Drug Administration (FDA) has banned the use of sulfites as a preservative for fruits and vegetables, but they are still in use in some foods.
Food allergies and sensitivities can produce a wide range of symptoms involving the skin, respiratory system, and nervous system. Children may have watery eyes, runny noses, and sneezing.
Skin rashes or hives can range from measles-like rashes to itchy welts. The rashes or welts can appear on a specific part of the body or can be widespread. Some children have swelling of the eyes, lips, and/or tongue.
Symptoms vary among children, even those who are sensitive to the same food. One child's specific reaction to an offending food does not mean that all children react the same. Nut allergies and shellfish, however, seem to be the most documented triggers for anaphylaxis. Nevertheless, anaphylaxis is not limited to those foods. IgE-mediated allergic reactions can progress to other allergic symptoms. For example, a child who has had hives is at risk for angioedema (swelling of the blood vessels) and anaphylaxis.
Symptoms also vary in intensity and by the amount eaten. One child may have a mild rash on the forearms when eating half a dozen strawberries. Another may be covered with a rash after eating only one. This variation is individualized and is a factor in the body's sensitivity to the target food.
Although the time between ingestion and symptoms is somewhat variable for allergic reactions (IgE-mediated), the vast majority occur within minutes. Nearly all occur within two hours. Reactions due to intolerances, like lactose, may occur somewhat later. Symptoms occurring days after a food is ingested are not likely related to the food.
The only treatment for IgE-mediated reactions to foods is avoidance. These reactions, as well as intolerances, are not responsive to desensitization. An epi-pen should be kept in the home for all IgE mediated food allergies and all inadvertent reactions should be treated.
It is not unusual for children to crave the very foods to which they are allergic. When the child is placed on an elimination diet, often the body will rebel at not being given the foods that cause it to react and will produce cravings for those foods.
Children are known to outgrow milk allergies in most cases, but—for safety purposes—reintroduction in a medical setting is advised. Egg allergy disappearance is not as high as it is for milk allergy. Sensitivities to wheat and soy are also outgrown. Allergies to peanuts, shellfish, and other foods that can produce anaphylaxis usually remain with the child throughout life.
If both parents have food allergies, precautions should be taken to minimize the risk of the child having a food allergy, too. Before birth and while breastfeeding, the mother can limit the baby's exposure to allergens by not bingeing on foods known to cause allergies. Breast-feeding delays the onset of allergies, but does not avoid them. The secretory IgA in breast milk fights infection but is not shown to avoid absorption of allergies.
Solid foods are slowly introduced at four to six months of age. The first solid foods should be those that have shown the potential for not producing an allergic reaction, such as fruits (except citrus fruits and berries), vegetables, and rice. Early introduction of highly allergenic foods may predispose a child to reactions, but this is controversial. It is recommended that parents avoid feeding the child highly allergenic foods until three years of age, if possible. The list of highly allergenic foods includes nuts, peanuts, fish, shellfish, and eggs. Whole cow's milk—not cow's milk formula—should be avoided during the first year. Having the child eat a variety of foods will also keep the child from too much exposure to any one particular food family.