1298 CMAJ, November 17, 2015, 187 (17)(adjusted odds ratio [OR] 1.6 [95% CI 1.0–2.6] for introduction at 10–12 months; adjusted OR 3.4 [95% CI 1.8–6.5] for introduction after 12 months). 11 In the same year, a prospective study involving more than 13 000 infants noted that early exposure to cow’s milk (within the first two weeks of life compared with age 105–194 days) was protective against cow’s milk allergy (p< 0.001). 12 Analysis of data from a large prospective birth cohort including more than 2500 infants in the Netherlands showed delayed introduction of foods to be associated with eczema and atopy at the age of two years. 13 In addition, a retrospective database review including all children born in Manitoba in 1995 found no increased risk of food allergy in premature or low-birthweight children, which refuted the notion that immune system and gastrointestinal tract immaturity increased the risk of food allergy. 14 In addition to emerging studies that showed that later introduction may be associated with increased risk of allergy, the “dual allergen exposure hypothesis” as an explanation of the causal mechanism of food allergy was proposed by Dr. Gideon Lack. According to his theory, gastrointestinal (GI) exposure (ie, food consumption) is protective against developing food allergy. The mechanism is thought to relate to the GI tract’s function in encouraging immune tolerance. The immune response resulting from cutaneous exposure to an antigen may lead to sensitization, especially in the presence of atopic dermatitis. 15 Further supporting this hypothesis, a mutation associated with loss of function of the gene encoding filaggrin, a protein involved in skin barrier protection, was discovered. 16 The mutation is present in about 50% of patients with eczema. 16 Filaggrin mutations have also been linked with peanut allergy. 17

As a result of these new data, the American Academy of Pediatrics released an updated position statement in 2008 that no longer recommended avoidance of any of the allergenic foods beyond the age of four to six months. 18 A guideline released in 2010 by the National Institute of Allergy and Infectious Diseases supported the