Scientists studying the effects of hormone-mimicking chemicals on humans have reported that compounds called phthalates, used in plastics and beauty products and widely found in people, seem to alter the reproductive organs of baby boys.
In the first study of humans exposed in the womb to phthalates, the researchers, who examined the genitalia of male babies and toddlers, found a strong relationship between the chemicals and subtle changes in the size and anatomy of the children's genitals. Phthalates are ubiquitous compounds used as softeners in plastics and to maintain color and fragrance in beauty products such as nail polish and perfume, among other uses.
It is the first time that scientists have shown that any industrial compound measured in mothers' bodies seems to disrupt the reproductive systems of their babies.
But many experts, including the authors of the report published today in the online version of the journal Environmental Health Perspectives, say that more research must be done to determine if the genital abnormalities in the boys lead to fertility or health problems and to prove that they are caused by phthalates.
For The Record
Los Angeles Times Saturday May 28, 2005 Home Edition Main News Part A Page 2 National Desk 1 inches; 54 words Type of Material: Correction
Genital abnormalities -- An article in Friday's Section A about a study linking phthalates, compounds used in plastics and cosmetics, with genital abnormalities in boys stated that Europe had prohibited using phthalates in cosmetics. Europe has banned two major types of the compounds in cosmetics, but other phthalates are still legal in the products.
The findings were based on tests of 85 mothers and sons, averaging nearly 13 months of age, born in Los Angeles, Minneapolis and Columbia, Mo. Mothers with the highest levels of chemicals in their urine late in their pregnancies had babies with a cluster of effects. The span between anus and penis, called anogenital distance, was comparatively short, and the infants had smaller penises and scrotums and more instances of incomplete descent of testicles.
Medical experts do not know whether babies with those physical characteristics will later develop reproductive problems. But in newborn animals, laboratory studies show that that combination of effects can lead to lower sperm counts, infertility, reduced testosterone and testicular abnormalities when they mature.
"In rats, it's called the phthalate syndrome. What we found for the first time is evidence for this syndrome in humans," said Dr. Shanna Swan, the study's lead researcher and a professor in the Department of Obstetrics and Gynecology at the University of Rochester School of Medicine and Dentistry. "Animals [exposed to phthalates] definitely have decreased testosterone, so it is likely that this is happening in humans too."
The study is the strongest evidence yet that man-made chemicals in the environment can feminize male babies in the womb.
Yet scientists say a larger study of babies should be conducted, and that they should be followed into adulthood to see whether they develop low sperm counts or any other reproductive problems.
"It's such an important observation, you'd like to see this done again with more children and another population," said Earl Gray, a U.S. Environmental Protection Agency reproductive toxicologist whose research has found that phthalates feminize male rodents.
"And we would like to see what the consequences are when they reach adulthood," Gray said. "We don't know the significance of this effect on the children later in life, but we do know the effect on rats."
"The main thing is this is a very small group of subjects. It is too early to say whether there are long-term effects, and whether this [anogenital] measure is important or not in humans," said Dr. Catherine Mao, a co-author and pediatric endocrinologist at the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center.
Reproductive biologists say that a shorter anogenital distance is a female-like effect in animals, a telltale sign of decreased male hormones, and that it is likely that the human effects are similar, because hormones function the same in animals and people.
If a child has a shorter anogenital distance, "you are very likely going to see changes in every other aspect of masculinization as well," said Frederick vom Saal, a reproductive toxicologist at the University of Missouri at Columbia.
Toxicologists have known since the early 1990s that some pesticides and industrial compounds, including phthalates, can mimic estrogen or block testosterone, the female and male sex hormones that control reproductive development. While they have found effects on the genitalia of laboratory animals and wildlife, they have been uncertain whether exposure to the fake hormones affects humans.
Some medical experts suspect that chemicals are responsible for reduced sperm counts that have been reported in much of the developed world, as well as increases in testicular cancer and cryptorchidism, or undescended testes. Three previous studies of men, two in the Boston area and one in India, linked phthalates to low sperm quality.