Something in the environment is driving the allergic epidemic, researchers say. The findings were exciting because they provided solid evidence that "there's something in the environment that's driving this allergic epidemic", Murdoch Childrens Research Institute researcher Professor Katie Allen told ABC News. Admissions to hospital in Australia due to anaphylactic shock have tripled over 13 years. They have increased more than sevenfold among children aged five to 14. Allergies to peanuts are the most persistent and dangerous allergies, with the highest lifetime risk for anaphylaxis. The study also found children from urban areas - such as Melbourne, which has been dubbed the "allergy capital of the world" - are more likely to have a nut allergy than children from rural regions. Nut allergies were also more common among children of mothers with higher education and socio-economic status. Some of this was attributed to higher reporting rates by parents who are more likely to seek help.

Researchers analysed the results of school entry health reports completed by the parents of 57,000 children, a report filled out by a parent or guardian about their child's health and wellbeing at the beginning of primary school in Victoria. Of the 57,000 respondents, 2892 parents reported a food allergy (5 per cent) and 1761 reported a nut allergy (3.1 per cent). While Australian-born children of Asian descent were more likely to have nut allergy than non-Asian children, children born in Asia who migrated to Australia were at decreased risk. Professor Allen said that migration from Asia after the early-infant period appeared to be a protective factor against the development of nut allergy. "We know there are rising rates of migration from East Asia to Australia," she said. "Our finding that migration from Asia to Australia after birth can protect against early onset allergic disease such as food allergy provides a potent clue for us to follow when trying to understand why food allergy is on the rise," she said.

Removing children from the Asian environment, or conversely exposing them to environmental risk factors in our Western environment - such as diet changes, microbial and UV exposure - uncovered a genetically determined risk of food allergy in children of Asian descent. Professor Allen said the overall presence of nut allergy in metropolitan Melbourne was 3.4 per cent, compared with 2.38 per cent in non-metropolitan areas. "While the question still remains as to why allergy rates are on the rise, the urban-rural difference could be down to the hygiene hypothesis, which raises the possibility that our urban environment with less diverse microbial exposure may contribute to the rise in allergies," Professor Allen said. "It strongly suggests that early life environmental factors linked to the modern lifestyle play a key role in allergy development. Understanding these factors better will provide opportunities to intervene to prevent food allergy in the future." The analysis of the School Entrant Health Questionnaire also revealed that nut allergy was more commonly reported among children of mothers with higher education levels, and a high socio-economic index.

In the paper, published in Clinical and Experimental Allergy, the research team suggest that mothers with higher levels of education and income from urban areas were more likely to seek medical advice for a food reaction and therefore more likely to report a nut allergy in their child. The study builds on more than a decade of leading allergy research by the Murdoch Childrens Research Institute. This is the first large, population-based study to show the prevalence of nut allergy, with data captured from the majority of children who began school in Victoria in 2010. Previous research from the HealthNuts study found "unexpectedly high rates" of nut allergy in Melbourne. As many as 3 per cent of one-year-old infants had a peanut allergy during medically supervised food challenges.