A food allergy occurs when an individual’s immune system mistakes a food protein (called an allergen) for a foreign substance. During an allergic reaction, the immune cells overreact to substances that are normally harmless and the body releases chemicals that trigger symptoms that can than affect the eyes, nose, and throat, as well as the skin and the lungs. Even a trace amount of the allergen can cause a reaction in sensitive individuals.
Food allergy is usually common among people who have family histories of allergies. About eight percent of children (compared to only two percent of adults) in the United States are estimated to have food allergies. Food allergies are most common during the first few years of life, and as the immune system continues to develop, allergic sensitivity declines over the first decade of life for most children.
According to the American Academy of Allergy Asthma & Immunology (AAAAAI), six foods cause 90% of food allergies in children. These six foods are milk, peanuts, soy, eggs, wheat, and tree nuts (such as pecans and walnuts). Children usually outgrow allergies to milk, eggs, and soy. However, allergies to peanuts, tree nuts, fish, and shellfish continue throughout adulthood.
Risk factors: Children with skin disorders, such as eczema, which causes itching, scaling, and thickening of the skin, or psoriasis, which causes, dry, red patches of skin, are more likely to develop food allergies. In fact, food allergies are seen in about 35% of children with eczema.
Children who have allergic reactions to inhaled substances, such as dust, mold spores, or pollen, also have an increased risk of developing food allergies.
Even exposing children to trace amounts of peanut protein or peanut oil products may cause peanut allergies in children, according to one study. Because peanut allergies are among the most common and severe food allergies, the American Academy of Pediatrics recommends that children with histories of food allergies do not consume peanuts or peanut-containing products until they are three years old. Strawberries should also be avoided until the baby is about 10-12 months old.
Children whose mothers have food allergies may be more likely to inherit the allergy if born by cesarean section, according to one study. One study of children with allergic mothers who had C-section deliveries found that the babies were seven times more likely to develop food allergies than predisposed children who were born vaginally. Although the reason for this is not clear, it has been suggested that cesarean deliveries might delay the colonization of the newborn intestine.
Causes: Most allergies are inherited, which means they are passed on to children by their parents. Although people inherit a tendency to be allergic, they may not inherit an allergy to the same allergen. When one parent has allergies, each of his/her children has a 50% chance of developing allergies. That risk increases to 75% if both parents have allergies.
The first, or several times after the body is exposed to nickel, the immune system becomes sensitized. During this process, the body’s white blood cells develop immunoglobulin E (IgE) antibodies, which are proteins that are specialized to quickly detect and bind to the food allergens when they enter the body. These antibodies also trigger the release of chemicals (such as histamine) that cause allergic symptoms, such as red, itchy, and swollen skin.
In some food groups, especially tree nuts and seafood, an allergy to one food may cause the patient to be allergic to all the members of the same group. This is known as cross-reactivity. However, it is also possible to be allergic to both peanuts and walnuts, which are from different food families. This is because the allergens for these products are very similar.
Cross-reactivity is not as common in the meat food group. For instance, many patients who are allergic to eggs can eat chicken, and many patients who are allergic to cow’s milk can eat beef.
Symptoms: Food allergy symptoms vary among patients. Symptoms can develop anywhere from several minutes to several hours after ingestion. Reactions usually lasts several hours. Hives are the most common allergic skin reaction associated with food allergies. Hives are red, itchy, swollen welts on the skin that may appear suddenly and disappear quickly. They often develop in clusters, with new clusters appearing as other areas clear up. The most severe type of reaction is called anaphylaxis because it causes low blood pressure and swollen airways. The most dangerous symptoms of anaphylaxis are low blood pressure, breathing difficulties, shock, and loss of consciousness, all of which can be fatal. Asthma symptoms, including coughing, wheezing, shortness of breath, or difficulty breathing, may be triggered by food allergies, especially in infants and young children. Eczema, which is itchy, scaly, red skin, may also be triggered by food allergies. Others may experience itchy skin or facial flushing. Gastrointestinal symptoms may include vomiting, diarrhea, gas, and abdominal cramping. Some patients may develop a red rash around the mouth, as well as swelling of the mouth, stomach, and throat.