Anaphylaxis is a rapid, life-threatening allergic reaction in which an allergen triggers a cascade of inflammation that affects the skin and the respiratory, cardiovascular, and gastrointestinal systems. Common triggers include certain foods (such as eggs, peanuts, dairy products, fish and shellfish, and tree nuts), drugs, blood products, dyes, and insect stings.
- Flushing of the skin
- Difficulty breathing
- Nausea or vomiting
- Profuse sweating
- Low blood pressure
- Change of mental status
- History of allergic disease, including asthma and eczema (a skin disorder characterized by inflammation, itching, and the formation of scales)
- History of exposure to allergens
- History of anaphylaxis: Previous (especially recent) anaphylaxis is a risk factor for recurrence.
Anaphylaxis and Food Allergy: Diagnosis and Treatment
- A medical history and physical examination are the most important steps.
- Skin or blood testing can be used to identify allergenic foods. In addition, a placebo-controlled food challenge can be used. In this test, which is done under medical supervision, the patient eats a small amount of the food allergen, as well as a placebo, to establish whether a food allergy really exists.
- Immediate medical attention may be required. Hospitalization and possibly intubation may be necessary for severe cases.
- The inciting agent should be removed, if possible. A tourniquet above the site of a venom sting or site of an allergy shot injection may be helpful.
- An epinephrine shot can be used for mild to moderate symptoms. Epinephrine should be administered as soon as the diagnosis of anaphylaxis is considered. It may be self-administered with an EpiPen or similar device and can be repeated at 15-minute intervals en route to an emergency department.
- Antihistamine medications (e.g., diphenhydramine (Benadryl), loratadine (Claritin), and ranitidine (Zantac)) should be used until anaphylaxis resolves. In addition, intravenous steroids are usually used in moderate and severe cases.
- Asthma inhalers may be used if wheezing occurs.
- If the patient has low blood pressure, immediate administration of intravenous fluids and various medications (e.g., dopamine, norepinephrine, phenylephrine, and vasopressin) may be life-saving.
- Patients with more than mild symptoms should be observed in the emergency department or admitted to the hospital for continued observation.
Anaphylaxis and Food Allergy: Nutritional Considerations
Allergic Reactions to Foods: Approximately 5 to 10 percent of young children are allergic to one or more foods. The risk for developing an allergy may be reduced by delaying the introduction of potentially allergenic foods and by avoiding foods that are allergenic to a child's parents.
Although allergic reactions can occur with almost any food, certain items, such as cow's milk, eggs, and nuts, are frequent causes in children, whereas peanuts, tree nuts, fish, and shellfish are the most common in adults.
Most children outgrow their food allergies, leaving 1 to 2 percent of adults with food allergies. Elimination of foods that commonly elicit food allergy and the use of hypoallergenic diets and food-elimination diets can help to identify or eliminate allergens.
- Common allergens include milk, eggs, peanuts, tree nuts, seeds, wheat, soy, fish, and shellfish. Since these foods are responsible for the vast majority of food allergy reactions, avoidance or delayed introduction of them may prevent an allergy. Allergic reactions to these foods have been implicated in food-induced asthma, and cow's milk allergy may also contribute to both ear infections and lung disease. Some individuals react to the presence of the allergens in these foods in amounts as low as 1 milligram.
- Fruits and vegetables may occasionally cause food allergy. Many healthful foods, vegetables among them, may cause food allergy. Allergy to celery and zucchini may remain even after thorough cooking. As noted below, individuals with pollen allergy often cross-react to many foods.
- Allergies may develop as a result of cross-reactivity to foods with similar antigens. Melon frequently elicits allergic reactions, including anaphylaxis, in people with pollen allergies and is highly cross-reactive with allergy to peaches.
Adults with birch pollen allergy and eczema may exhibit allergic reactions to foods that cross-react with birch pollen: for example, apple, apricot, carrot, celery, cherry, hazelnut, and pear.
Persons who are allergic to one fruit are often allergic to others in the same family. Peach, melon, kiwi, apple, and banana accounted for 72 percent of allergic reactions in a group of adults with Rosacea fruit allergy.
People allergic to latex are often allergic to tropical fruits, such as bananas, kiwi, and avocado.
A lower frequency of allergic cross-reactivity occurs with the ingestion of plant foods than with the consumption of animal products. The frequency between peanuts and other legumes is less than 10 percent, and between wheat and other grains, the frequency is less than 15 percent. By comparison, cross-reactivity of mammalian milks (i.e., switching from cow's milk to goat's milk) occurs in approximately 90 percent of cases, and occurs between types of fish with a frequency of 50 percent.
Reducing the Likelihood of Allergies
The following steps may help reduce the likelihood that children will develop allergies.
- Breast-feeding: Most studies show a protective effect of breast-feeding. In addition, in infants at risk for allergies, maternal avoidance of allergenic foods during the first six months of breast-feeding reduces the incidence of food allergy.
If mothers cannot breast-feed, formula should be chosen carefully. Cow's milk allergy is common and often occurs even with partially and extensively hydrolyzed whey formulas. An amino acid-based formula, on the other hand, was found to be nonallergenic. Soy-based formulas are free of cow's milk proteins, but can elicit allergies of their own in some children.
- Delayed introduction of potentially allergenic foods: In addition to introducing table foods no earlier than four to six months of age, avoidance of eggs and fish until at least one year (if used at all) and of nuts until at least age two or three is recommended.
- Caution regarding processed foods that may harbor many potential allergens: Individuals may be allergic to several foods and food ingredients, and processed food products can be especially problematic. These foods often contain milk, egg, fish, beef, nuts, and seed proteins that are not listed on the product labels. Although processing of certain foods reduces their allergenicity (e.g., cutting or heating fruit), most allergens remain stable after processing. Eating unprocessed, minimally processed, and homemade foods is likely to decrease this risk. In individuals who suspect but cannot confirm food allergy, an elimination diet can be helpful (see below).
Although further studies are needed for confirmation, use of an allergen-avoidance diet for high-risk women during breast-feeding may reduce children's risk of developing eczema. Further, use of elimination diets for infants, children, and adults with food allergy and eczema may be helpful.
More than 50 percent of children experience significant improvements in eczema during dietary elimination periods, and roughly one-third outgrow their allergies after one to two years of avoiding the offending foods. An elimination diet can be easily done on an outpatient basis, when patients can control their diet for several weeks. The procedure is described below.
- Start with a baseline diet made up of only those foods not implicated in food allergy. Well-tolerated foods include:
- Brown or white rice, puffed rice
- Cooked or dried fruits: cherries, cranberries, pears, prunes, peaches, apricots, papaya, and plums, unless there is a documented allergy to these or to birch pollen.
- Cooked green, yellow, and orange vegetables: artichokes, asparagus, broccoli, chard, collards, lettuce, spinach, squash, string beans, sweet potatoes, tapioca, and taro.
- Water, plain or carbonated
- Condiments: modest amounts of salt, maple syrup, vanilla extract.
- When the allergic symptoms have abated (usually within a week or so), the patient should keep a food diary and add in foods one food group at a time. Foods should be added in generous amounts every three to five days to observe which cause symptom recurrence. Foods listed above that are most commonly implicated in food allergy should be added last.
- If the food is associated with allergy symptoms, it should be removed from the diet for one to two weeks, and reintroduced to see if the same reaction occurs. If no symptoms are experienced, that food can be kept in the diet. For individuals with a history of anaphylaxis, foods should only be tried under the close supervision of a qualified physician.