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A controversial chemical used in Teflon non-stick coatings could be making people more prone to allergies, a study suggests.

Perfluoro-octanoic acid (PFOA) - also used to make all-weather clothing and stain-resistant fabrics and carpets - has already been identified by scientists as "likely" to be carcinogenic to humans.

Now Dr Jean Meade and colleagues at the National Institute for Occupational Safety and Health in Morgantown, West Virginia, have shown it may prime the immune system to overreact to allergy triggers (allergens) such as dust mite or dander.

Lab mice given PFOA before being exposed to an egg allergen produced more antibodies and experienced more constriction of their airways than those exposed to the allergen alone.

The results published in Toxicological Sciences suggest one possible explanation for the rising incidence of asthma in children.

The authors compared three major immune responses in mice subjected to an allergen alone, environmental chemical PFOA alone and the two together.

They measured antibody response levels, airway hypersensitivity response, and lung and immune system tissue structure.

Mice were treated on the skin on the back of their ears with PFOA for 4 days then exposed to the foreign egg antigen ovalbumin (egg white) or a control.

The mice treated with the PFOA were more likely to have an alleric reaction to the egg.

The PFOA doses, ranging from 12.5 to 50 milligrams per kilogram (mg/kg), are comparable to those used in similar studies but are considerably higher than those to which humans are likely exposed.

Over the past five decades PFOA has become so widespread a contaminant that almost everyone tested has measurable amounts in their bodies.

Indeed a recent study by scientists at John Hopkins University, Baltimore, found 100% of local newborns were contaminated by PFOA.

Researchers have become increasingly alarmed as numerous studies have shown that PFOA and related chemicals are commonly found in people.

On average levels of these chemicals in human blood are relatively low ranging from about 4 to 7 parts per billion (ppb) but widespread contamination raises concerns about the potential harmful health effects.

PFOAs can contribute to thyroid problems, immune changes and testicular, liver and pancreatic cancer in laboratory animals. People exposed to PFOA at work may be at higher risk for pancreas, testis and prostate cancers.

Dr Meade said: "These studies were conducted to investigate the role of skin exposure to Perfluorooctanoic acid (PFOA), a known immunosuppressant, on the hypersensitivity response to ovalbumin in a mouse model of asthma.

"In a mouse model PFOA was demonstrated to be immunotoxic following skin exposure with an enhancement of the hypersensitivity response to ovalbumin suggesting PFOA exposure may augment the IgE response to environmental allergens."

Dr Robert Rickard - a science director at US chemicals giant DuPont which makes Teflon plastic coatings - says PFOA is unlikely to cause allergy-related problems in humans but admits no studies have looked at this question.

PFOA is found in the blood of almost everyone yet how it gets there is a mystery. It should not turn up in final manufactured products although DuPont has measured very small amounts in treated carpets and upholstery.

Heat-resistant Teflon was discovered purely by accident by DuPont chemist Roy Plunkett in 1938. In 1960 the U.S. Food and Drug Administration approved it for use in cookware.

But when it is heated to over 600° the coating can break down and release PFOA.

In 2004 the company agreed an out-of-court settlement in a class action lawsuit brought by about 50,000 residents who lived near its West Virginia plant.

The residents, who lived along the Ohio river south of Parkersburg, West Virginia, claimed the company had contaminated local water supplies with PFOA.

They alleged the chemical was linked to birth defects and other health hazards.

DuPont eventually agreed to pay $50m in cash to the plaintiffs, plus $22m in legal costs. It also agreed to spend $10m on special water treatment facilities to filter out PFOA.

But DuPont did not accept liability and has maintained that PFOA does not pose any danger to the public.

An estimated one in eight British children suffers from asthma while one in five has been diagnosed with the condition at some stage in their lives.

Significant risk factors include obesity, genetic predisposition, smoking, low birth weight, air pollution and allergens such as exhaust particles, smoke and household dust mites.