Children living in towns and cities are more likely to be allergic to milk, eggs and peanuts than their country cousins, according to a new study.
Scientists at Johns Hopkins University in the US said one in ten urban kids had major food allergy - and the true figure could be even higher.
The research builds on a British study which found children born in densely populated areas more than twice as likely to have a peanut or shellfish intolerance than those born in sparser regions.
The authors suspect exposure to pollutants might be to blame – especially for children who have not built up immunities from common bacteria which are prevalent in nature but rare in the concrete jungle.
Dr Robert Wood said: “Our findings are a wake-up call, signalling an urgent need to unravel the causes, contributors and mechanisms that drive the high prevalence of food allergies among an already vulnerable group known for its high risk of asthma and environmental allergies.”
The researchers tracked the first five years of 516 children living in Baltimore, Boston, New York City and St. Louis, measuring their exposure to allergens each year while tracking their diets and general health.
While nearly 10 per cent of them had full-blown allergies to milk, eggs or peanuts, more than half – 55 per cent – were classified as ‘sensitive’ to the foods.
Breastfed children were at even higher risk, but children living with higher levels of endotoxin – a chemical released by many bacteria – were partially shielded.
That detail will galvanise proponents of the ‘hygiene hypothesis’ which says exposure to microbes at an early age can help build up the child’s defences against asthma and allergies.
City children are already far more likely to suffer environmental allergies such as pollen and mildew, as well as asthma, which has been linked to early use of antibiotics, delivery by Cesarean section, and affluence.