controversial chemical.

Baby boys are more likely to have changes in their genitals — such as undescended testicles and smaller penises — if their mothers were exposed to high levels of a controversial chemical during pregnancy, a new study shows. Virtually everyone has been exposed to the chemicals, called phthalates, which are used in countless plastic products and are found in everything from drinking water to breast milk to household dust, according to the study, published in the current issue of Environmental Research.

Until recently, most studies have been conducted in animals. Those tests suggest that phthalates interfere with the male sex hormone testosterone, causing a "phthalate syndrome" in male fetuses that changes the way their genitals develop, says study author Shanna Swan, a professor at the University of Rochester School of Medicine and Dentistry.

Swan says her study of 106 mothers and sons suggests this syndrome may be occurring in humans, too. In her study, doctors measured phthalate levels in the mothers' urine during pregnancy, then examined the babies at 12 months.

Boys whose mothers had the highest phthalate levels were more likely than others to show three anatomic differences: smaller penises, a shorter distance between the anus and base of the penis, and undescended or incompletely descended testicles, Swan says. Swan also notes that most boys had normal sex organs. Twelve had incompletely descended testicles, while 29 babies fell into a category with "shorter" anogenital distances.

In most cases, these aren't serious problems, Swan says. Babies with undescended testicles often need no treatment, because the organs descend on their own by age 1. Others can be helped with hormone treatments or surgery. And even the smaller penises appeared to be within the normal range.

But Swan says she's concerned that these changes indicate a deeper problem — that phthalates may have made the boys "less masculine" in key ways. In animals, males with these genital changes also had lower sperm counts, she says.

Swan says she is also concerned about girls. It's possible that any effects from pre-birth phthalate exposure may not surface until the girls hit puberty or try to have children, she says.

In her paper, she notes that other researchers have linked phthalates to reduced sperm quality and DNA damage, as well as hormone changes, reduced lung function and premature puberty.

Baby boys are more likely to have changes in their genitals — such as undescended testicles and smaller penises — if their mothers were exposed to high levels of a controversial chemical during pregnancy, a new study shows. Virtually everyone has been exposed to the chemicals, called phthalates, which are used in countless plastic products and are found in everything from drinking water to breast milk to household dust, according to the study, published in the current issue of Environmental Research.

Until recently, most studies have been conducted in animals. Those tests suggest that phthalates interfere with the male sex hormone testosterone, causing a "phthalate syndrome" in male fetuses that changes the way their genitals develop, says study author Shanna Swan, a professor at the University of Rochester School of Medicine and Dentistry.

Swan says her study of 106 mothers and sons suggests this syndrome may be occurring in humans, too. In her study, doctors measured phthalate levels in the mothers' urine during pregnancy, then examined the babies at 12 months.

Boys whose mothers had the highest phthalate levels were more likely than others to show three anatomic differences: smaller penises, a shorter distance between the anus and base of the penis, and undescended or incompletely descended testicles, Swan says. Swan also notes that most boys had normal sex organs. Twelve had incompletely descended testicles, while 29 babies fell into a category with "shorter" anogenital distances.

In most cases, these aren't serious problems, Swan says. Babies with undescended testicles often need no treatment, because the organs descend on their own by age 1. Others can be helped with hormone treatments or surgery. And even the smaller penises appeared to be within the normal range.

But Swan says she's concerned that these changes indicate a deeper problem — that phthalates may have made the boys "less masculine" in key ways. In animals, males with these genital changes also had lower sperm counts, she says.

Swan says she is also concerned about girls. It's possible that any effects from pre-birth phthalate exposure may not surface until the girls hit puberty or try to have children, she says.

In her paper, she notes that other researchers have linked phthalates to reduced sperm quality and DNA damage, as well as hormone changes, reduced lung function and premature puberty.