The past three years have seen significant advances in "epidemiological evidence and the development of animal models" to help understand how endocrine disruptors work, says Kenneth Korach, director of the Environmental Disease and Medicine Programme at the National Institute of Environmental Heath Sciences.

The mean of exposures to endocrine disruptors can be difficult to determine. "it's not like smoking was," says Swan, who did the phthalates research.

"They're all around us, in food, in house hold dust and in product, but they're exposed. Our old epidemiological tools - interviews, looking at medical records and questionnaires - are useless. We have to look at the body. But it's expensive and hard to get people to give blood."

And if figuring out what a tiny amount of one chemical does is hard, researchers say they have almost no idea what happens when many chemical interact. "Nobody's exposed to one thing," Korach says, " The problem is we haven't done enough yet to look at combinations."

The Big Picture
Of course, each of these studies is only one small piece in a much larger puzzle that still must be filled out, says Earl Gray, a senior research biologist with EPA's endocrinology branch. "There are things that we know for sure," he says. "It's obvious and has been for a long time that there are effect in wildlife due to endocrine-disrupting chemicals."

In humans, the evidence isn't clearcut: "A single stuffy doesn't create a disaster, it's a hypothesis that needs to be replicated."

Others wonder why compound are turning up harmful in some studies, while "every test we've ever done in the past says they're inactive," says James Lamb of scientist and engineering consulting firm Blasland, Bouck & Lee Inc.