NEW YORK, Feb. 5 -- Call these chemicals "his" and "her" endocrine disruptors.
Although they have been linked to reproductive problems in both sexes, bisphenol A (BPA) and phthalates -- common chemicals found in household plastics -- have gender-specific effects.
BPA mimics estrogen, while phthalates block testosterone action, Hugh S. Taylor, M.D., of Yale University, said at a press briefing.
"BPA looks like estrogen," Dr. Taylor, whose research focuses on uterine development and endocrine disruption, said of its chemical structure. "By itself it is a very weak estrogen."
The chemical stimulates uterine growth, he said, and animal studies have revealed other estrogen-like effects.
Mice that were exposed to BPA as fetuses developed abnormalities of the ovaries, uterus, and vagina, Dr. Taylor said. Other murine studies found genetic abnormalities in eggs, an increased risk of mammary cancers, and early puberty in females.
The list of problems was shorter for male mice exposed to the chemical, with reduced sperm production and increased prostate size at the top.
Although fewer human studies have been done, they've found an association between BPA exposure and increased risk of miscarriage and polycystic ovary disease, Dr. Taylor said.
Phthalates, on the other hand, have antiandrogenic effects, Dr. Taylor said.
Studies in male animals have found reduced sperm production, undescended testes, hypospadias, decreased testosterone production, and reduced anogenital distance.
The chemical's effects on female reproduction were far fewer, with murine studies linking it to delayed or premature puberty.
Human studies of phthalates are few, but most have found an association between exposure and male reproductive diseases similar to those in the mouse models.
Dr. Taylor said phthalates -- plasticizers used to produce soft and flexible materials -- are more widespread than BPA, found in everything from food packaging and building materials to shower curtains and cosmetics.
In December 2008, the National Research Council called on the FDA to investigate whether or not phthalates pose a threat to human health. The request came a few months after the FDA had been lambasted for its initial decision that BPA was safe.
The agency is currently re-evaluating its stance, although one of its original reasons for not ruling against the chemical was insufficient evidence.
Dr. Taylor said it's hard to do adequate human studies of chemicals like BPA and phthalates for two reasons. First, the entire population is exposed, so there is no control group. And, ostensibly, it would be unethical to do a study that involves exposing humans to high levels of potential toxins.
Research has shown that even low levels of BPA and phthalates cause problems in humans -- including obesity, said Robert H. Lustig, M.D., of the University of California San Francisco, who studies a number of chemicals commonly found in the environment and their effects on human health.
"Sometimes you just have to make decisions based on 'inadequate' evidence," Dr. Lustig said regarding the FDA's investigation of BPA, and potentially phthalates. "You just [make them] based on the right thing to do."