The CDC concludes that the prevalence of food allergy in children younger than 18 years increased by 18% from 1997 through 2007.17,18 The cause of this increase is unclear but likely multifactorial; hypotheses include an increase in associated atopic conditions, delayed introduction of allergenic foods, and living in an overly sterile environment with reduced exposure to microbes.19 A recent population-based study of food allergy among children in Olmsted County, Minnesota, found that the incidence of food allergy increased between 2002 and 2007, stabilized subsequently, and appears to be declining among children 1 to 4 years of age, following a peak in 2006-2007.19
What are the risk factors?
Proposed risk factors for food allergy include demographics, genetics, a history of atopic disease, and environmental factors. Food allergy might be more common in boys than in girls, and in African Americans and Asians than in Whites.12,16 A child is 7 times more likely to be allergic to peanuts if a parent or sibling has peanut allergy.20 Infants and children with eczema or asthma are more likely to develop food allergy; the severity of eczema correlates with risk.12,20 Improvements in hygiene in Western societies have decreased the spread of infection, but this has been accompanied by a rise in atopic disease. In countries where health standards are poor and exposure to pathogens is greater, the prevalence of allergy is low.21
Conversely, increased microbial exposure might help protect against atopy via a pathway in which T-helper cells prevent pro-allergic immune development and keep harmless environmental exposures from becoming allergens.22 Attendance at daycare and exposure to farm animals early in life reduces the likelihood of atopic disease.16,21 The presence of a dog in the home lessens the probability of egg allergy in infants.23 Food allergy is less common in younger siblings than in first-born children, possibly due to younger siblings’ increased exposure to infection and alterations in the gut microbiome.23,24
Diagnosis: Established by presentation, positive testing
Onset of symptoms after exposure to a suspected food allergen almost always occurs within 2 hours and, typically, resolves within several hours. Symptoms should occur consistently after ingestion of the food allergen. Subsequent exposures can trigger more severe symptoms, depending on the amount, route, and duration of exposure to the allergen.25 Reactions typically follow ingestion or cutaneous exposures; inhalation rarely triggers a response.26 IgE-mediated release of histamine and other mediators from mast cells and basophils triggers reactions that typically involve one or more organ systems (Table 2).25
Cutaneous symptoms are the most common manifestations of food allergy, occurring in 70% to 80% of childhood reactions. Gastrointestinal and oral or respiratory symptoms occur in, respectively, 40% to 50% and 25% of allergic reactions to food. Cardiovascular symptoms develop in fewer than 10% of allergic reactions.26
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