YOLANDE Sprague could be forgiven for feeling virtuous. Four years ago, just after giving birth to her second child, the stay-at-home mom heard about BPA, a chemical inside some plastics that can leach into water or food slowly over time, potentially causing serious health problems like cancer.

Unwilling to take any risks, she ran to Babies "R" Us, which had a program to exchange baby bottles containing BPA, and walked out with US$100 in rebates.

If only life were so easy.

What Sprague didn't realize is that BPA, or bisphenol A, is ubiquitous. Simply put, just about anything you eat that comes out of a can - from Campbell's Chicken Soup and Spaghettis to Diet Coke and BumbleBee Tuna - contains the same exact chemical.

The exposure to BPA from canned food "is far more extensive" than from plastic bottles, said Shanna Swan, a professor and researcher at the University of Rochester in New York. "It's particularly concerning when it's lining infant formula cans."

BPA is the key compound in epoxy resin linings that keep food fresher longer and prevents it from interacting with metal and altering the taste. It has been linked in some studies of rats and mice to not only cancer but also obesity, diabetes and heart disease.

Trade groups for chemical and can manufacturers say they stand behind the chemical, and point to some studies from governmental health agencies that deem BPA safe and effective for food contact. They also note that its use has substantially reduced deaths from food poisoning.

But in January, the US Food and Drug Administration for the first time expressed "some concern" about BPA. Propelled in part by recent independent scientific studies and also bowing to mounting concern from the public and consumer groups, the agency announced that it would tap US$30 million in federal stimulus funds to study the chemical's potential effects on the human body.

Though it is not clear how economically stimulating the study will be, its results are anxiously awaited in industry and consumer circles. The report, due late in 2011, is being done in collaboration with the US National Institutes of Health.

"BPA has not been found or been proven to harm either children or adults, but because children ... in the very early stages of development are exposed to BPA, the data that we're getting deserves a much closer look," Deputy Health and Human Services Secretary Bill Corr said earlier this year.

What is clear, however, is that unlike the case with plastic, there are no economically viable alternatives to the chemical in epoxy resins right now.

"If it's in baby bottles, then I can imagine it's in a lot of other things," said Sprague, who has a history of premature deliveries, but is due to give birth to a boy in September. "Everybody gets breast cancer now. It's scary. Is it because of BPA? I don't know."

One scientist helping to lead the charge against BPA is Yale University physician, professor and researcher Hugh Taylor. His research has shown that the chemical alters the way genes react to estrogen, and could open the door for infants in utero to develop cancer much later in life.

"I tell my pregnant patients to avoid products containing it," he said. "Even a fleeting exposure in pregnancy can cause lasting damage."

The studies by Taylor are certainly eye-opening. They have shown that the chemical alters the way DNA operates, a process known as an epigenetic change.

On each strand of DNA a group of carbon molecules binds to receptors that help turn genes on or off. In the presence of BPA, though, many of those carbon molecules can be removed from DNA, and with them the switch.

Think of the carbon groups as a kind of lock, and the DNA receptors as a gate. When the lock is removed, the gate can swing open, greatly increasing the risk for estrogen to flow through later in life, interact with DNA and cause cancer.

"It has permanent, lasting effects," said Taylor, donning a white coat in his New Haven, Connecticut, lab surrounded by beakers, microscopes, pipettes and other tools of the scientist's trade. "The adult exposure is concerning, but I think the fetal exposure is worse."

To study the way BPA may affect children in utero, Taylor injected pregnant mice with high doses of the chemical five days into their 21-day gestation cycle. He found that the mice exposed to BPA in the womb lacked the "gate" on their DNA receptors and were more susceptible to estrogen for the rest of their lives.

Since many foods contain natural estrogen - soy, for instance - Taylor believes his studies suggest complications could arise down the road simply from eating basic foods, never mind estrogen supplements that many women take as they enter menopause. "In the mouse models, they're more prone to cancer," Taylor said.

As a gynecologist, Taylor studied the effects primarily on female mice. The long-term impact of increased BPA on DNA receptors in males, he said, remains unknown. His research is also limited because he can't test BPA on unaffected humans. "We all have it in our bodies, so there's no way to test a population without it," he said. "You'll never have the perfect experiment in humans to prove this."

Right now Taylor is studying just how BPA removes the carbon groups from DNA - in effect the specific process that removes the "lock" - and hopes this will shed further light on how the chemical interacts with the body.

He acknowledges BPA's role in food safety but says people should be made aware of the potential danger. "We always balance the risk with the benefits in our lives," he said. "There's a price we pay for modern society and convenience."

Frederick vom Saal, a professor at the University of Missouri who is studying BPA independently from Taylor, is far less diplomatic. Known as an aggressive crusader against the chemical, he said that if BPA were treated as a drug, "it would have been pulled immediately" by regulators.

Inside canned food, the thin layer of epoxy resin sits between the food and metal can, helping to keep the two from interacting and preventing rust.

The resin is sprayed into the can and dries almost instantly. Thousands of companies, such as Campbell Soup Co and Coca-Cola, use it to line their cans. Without it, food would perish far faster. Cans lacking the chemical would explode on store shelves when contents reacted with the metal.

First synthesized in 1891, BPA is a commercial hardener, making it great to use in a wide variety of applications, ranging from plastic canoes to headlights to cash register receipts. As a key building block for epoxy resin, it acts as part of the compound's polymer base, and was first used in the 1940s in canned foods.

A breakthrough product in its day, it has also been enduring. "There's just something about it," said Steve Russell, head of the plastics division for the American Chemistry Council (ACC), an industry trade group. "When they figured it out, it was one of those 'Eureka' moments."

For the time being, the chemical industry is not just sticking with BPA. It is also warning consumers to be wary of anything that claims to be an acceptable substitute but may not have undergone rigorous testing.

"We're all parents, and we can all understand that everybody wants to do the best for their kids," the ACC's Russell said. "But in doing so we need to understand that we're doing it not because government agencies say they're not safe, we're doing it because some people want to be extra safe."