A byproduct of chemicals used to help purify water could be to blame for a surge in food allergies, according to a study.
Researchers have found that people exposed to high levels of dichlorophenols, produced when chlorine is added to water to ensure it is free of bugs, tend to be more prone to food allergies too.
Elina Jerschow, assistant professor of allergy and immunology at the Albert Einstein College of Medicine in New York, said: “Our research shows that high levels of dichlorophenol-containing pesticides can possibly weaken food tolerance in some people, causing food allergy.
“This chemical is commonly found in pesticides used by farmers and consumer insect and weed control products, as well as tap water.”
Together with colleagues, she looked at the incidence of food allergies among 2,211 people who were participants in the US National Health and Nutrition Examination Survey.
Of those, the quarter with the highest level of dichlorophenols in their urine were looked at in detail.
The academics found their chance of having a food allergy - for example to eggs, peanuts, milk or shrimp - was 80 per cent higher than those with lower levels of dichlorophenols.
Writing in the journal Annals of Allergy, Asthma and Immunology, they concluded: "In this population, we found consistent associations between high levels of dichlorophenol exposure and a higher prevalence of food allergies.”
Among this group 550 or so people with the highest levels of the chemicals, their chance of having both a food allergy and an ‘environmental’ allergy - for example to pollen - was 61 per cent higher.
Dr Jerschow said: "Previous studies have shown that both food allergies and environmental pollution are increasing in the United States.
"The results of our study suggest these two trends might be linked, and that increased use of pesticides and other chemicals is associated with a higher prevalence of food allergies."
However, she said that further studies were necessary “to confirm this link”.
If firm evidence emerged that dichlorophenols triggered allergies, Dr Jerschow cautioned that avoiding tap water was unlikely to solve the problem.
Other dichlorophenol sources, such as pesticide-treated fruits and vegetables, may play a greater role in causing food allergy, she said.
Chlorophenols are a byproduct of chlorinating water. When the chlorinating agent is added, it reacts for phenols - organic compounds found in plants - which creates a range of chlorophenols.
According to the World Health Organisation, there are no guidelines for concentrations of dichlorophenols because data on toxicity “are limited”.
According to the Centres for Disease Control and Prevention, an increase in food allergy of 18 per cent was seen between 1997 and 2007. The most common food allergens are milk, eggs, peanuts, wheat, tree nuts, soy, fish, and shellfish.
Allergy experts agree that food allergies are also on the increase in Britain, and that this increase is not solely the result of people being more likely to report potential problems to their doctors.
A recent study conducted on the Isle of Wight found one in 20 children had a clinically confirmed allergy.
However, it is thought many people believe they suffer from a food allergy but actually do not.
In 2010 the National Institute for Health and Clinical Excellence (Nice) estimated that while more than a third of people believed they were allergic to some form of food, only a tenth actually were when properly tested.
A spokesman for Thames Water said: "We chlorinate water once it has been fully processed, so there is no organic matter in it."
By Stephen Adams Telegraph.co.uk