Previous research on animals has suggested phthalates may damage reproductive development by disrupting hormone levels.
Phthalates are used in the manufacture of plastics, lubricants and
solvents, and are found in cosmetics, medical equipment, toys, paints
The University of Rochester team, New York, found
exposure to the chemicals was linked to a higher risk of genital
abnormalities in baby boys.
The study features in the journal Environmental Health Perspectives.
But until now evidence of a similar effect on humans has proved inconclusive.
The Rochester team, who examined 134 boys, found women with higher
levels of phthalate-related chemicals in their blood were more likely
to give birth to boys with undescended, or small testicles, small
penises, or a shorter distance than usual between the genitals and
It did not take exceptional levels of exposure to
produce an effect - abnormalities were found in women exposed to levels
below those found in a quarter of US women.
Lead researcher Professor Shanna Swan said: "We were
able to show, even with our relatively small sample, that exposed boys
were likely to display a cluster of genital changes."
Professor Richard Sharpe, of the UK Medical Research
Council's Human Reproductive Science Unit in Edinburgh, said more work
was needed to confirm the results.
But he told BBC News website: "It is significant. It is
the first piece of evidence that we have that phthalates may cause
adverse effects on reproductive development in human foetuses."
Professor Sharpe said the chemicals appeared to suppress production of the male sex hormone testosterone.
"Testosterone is absolutely critical to development - most of the
things that make males different to females are down to pre-natal
exposure to the hormone.
"It is not just the effect on genital development, but also on tissues throughout the body, including the brain."
The conservation group WWF, which campaigns against harmful environmental chemicals, described the findings as "startling".
Gwynne Lyons, toxics advisor to WWF UK, said: "This research highlights
the need for tougher controls of gender bending chemicals.
"At the moment regulation of the chemicals industry is
woefully inadequate, and something needs to be done about this
The UK government is looking at how the regulation of
hormone-disrupting chemicals could be made more effective under a new
EU chemicals law.
Several types of phthalates have already been banned.
PRODUCTS CONTAINING PHTHALATES
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