Peanut allergy

Peanut allergy is a type of food allergy to peanuts. It is different from tree nut allergies, because peanuts are legumes and not true nuts. Symptoms of allergic reaction typically occur within 2 hours of peanut ingestion. Allergic symptoms can involve the skin (hives, swelling), gastrointestinal (vomiting, diarrhea), respiratory system (cough, wheeze) or cardiovascular system (drop in blood pressure, shock). Anaphylaxis may occur. The risk of death from anaphylaxis is low, approximately 1 in 10 million. It is due to a type I hypersensitivity reaction of the immune system in susceptible individuals. Prevention may be partly achieved through early introduction of peanuts to the diets of pregnant women and babies. It is recommended that babies at high risk be given peanut products in areas where medical care is available as early as 4 months of age. Oral immunotherapy results in some degree of tolerance in about 65% of children, though side effects are frequent. The principal treatment for anaphylaxis is the injection of epinephrine. Peanut allergy occurs in about 1.4–2% in Europe and the United States as of 2021, increasing 3.5-fold over the preceding two decades. Among children in the Western world, rates of peanut allergy are between approximately 1.5% and 3% and have increased over time. It is a common cause of food-related fatal and near-fatal allergic reactions.

Signs and symptoms

Most symptoms of peanut allergy are related to the action of immunoglobulin E (IgE) and other anaphylatoxins which act to release histamine and other mediator substances from mast cells (degranulation). In addition to other effects, histamine induces vasodilation of arterioles and constriction of bronchioles in the lungs, also known as bronchospasm. Symptoms of allergic reaction typically occur within 2 hours of peanut ingestion. Allergic symptoms can involve the skin (itchiness, hives, swelling), gastrointestinal (vomiting, diarrhea), respiratory system (cough, wheeze) or cardiovascular system (drop in blood pressure, shock). Anaphylaxis may occur. The risk of death from anaphylaxis is low, approximately 1 in 10 million.

Cross-reactivity with other food People with confirmed peanut allergy may have cross-reactivity to tree nut, soy, and other legumes, such as peas, lentils, and lupinus. The cause of cross-reactivity results from similarity in the structures of storage proteins between the food sources. Allergenic proteins are grouped by protein families: cupins, prolamins, profilin and others. Peanuts and soybeans have proteins in the cupin, prolamin, and profilin families, while lentils contain cupin proteins. A 2008 cohort study found no linkage between soy consumption and peanut allergy. Instead, the appearance of an association is likely due to confounding, as children with a milk allergy, who are at an increased risk of peanut allergy, are more likely to consume soy products. Reviews of human clinical trials report that 6–40% of people with a confirmed peanut allergy will have allergic symptoms when challenged with tree nuts or legumes.

Causes Oral consumption is the most common route of exposure, but topical (skin) and inhalation can also trigger minor allergic reactions. There are at least 11 peanut proteins identified as allergenic. The condition is associated with several specific proteins categorized according to four common food allergy superfamilies: Cupin (Ara h 1), Prolamin (Ara h 2, 6, 7, 9), Profilin (Ara h 5), and Bet v-1-related proteins (Ara h 8). Among these peanut allergens, Ara h 1, Ara h 2, Ara h 3 and Ara h 6 are considered to be major allergens which means that they trigger an immunological response in more than 50% of the allergic population. These peanut allergens mediate an immune response via release of Immunoglobulin E (IgE) antibody as part of the allergic reaction. Some of the peanut allergens can undergo enzymatic and non-enzymatic modifications, which makes them more likely to bind to ligands on antigen-presenting cells. Ara h 1 can undergo glycosylation modifications which have been shown to induce immunomodulatory responses; it stimulates lectin receptors MR and DC-SIGN on dendritic cells which further propagate cytokines and bias the immune system towards a Th2 type response. Peanut proteins that undergo non-enzymatic changes through Maillard reactions when cooked or exposed to room temperature have an increase in AGE modifications on their structure. These changes have been shown to stimulate RAGE receptors and SR-AI/II on dendritic cells and thus lead to an increase in IL-4 and IL-5-releasing Th2 cells. Peanut allergies are uncommon in children of developing countries where peanut products have been used to relieve malnutrition. The hygiene hypothesis proposes that the relatively low incidence of childhood peanut allergies in developing countries is a result of exposure to peanuts early in life, increasing immune capability.

Desensitization through exposure In infants with a family history of peanut allergy, consuming peanut proteins at 4 to 11 months old has been shown to reduce the risk of developing an allergic response by 11–25%. From these results, the American Academy of Pediatrics rescinded their recommendation to delay exposure to peanuts in children, also stating there is no reason to avoid peanuts during pregnancy or breastfeeding. A later study by the National Institutes of Health provided further evidence supporting this. The study involved giving children diagnosed as "high allergic" small portions of peanut flour daily for several years, with some children randomly assigned placebo flour. The results were 71% of the children receiving peanut flour became desensitized to peanuts, while 2% receiving placebo flour became desensitized.

Diet during pregnancy There is conflicting evidence on whether maternal diet during pregnancy has any effect on development of allergies due to a lack of good studies. A 2010 systematic review of clinical research indicated that there is insufficient evidence for whether maternal peanut exposure, or early consumption of peanuts by children, affects sensitivity for peanut allergy.

Routes of exposure

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