Enamel(釉质) is something hard covering a tooth. If it doesn’t form properly, a child can develop cavities(蛀牙) and other problems. A dentist can repair these defects. But there is no way to fix the changed gene instructions responsible for weakening the enamel in the first place. “This enamel defect now affects 15 to 20 percent of children aged 6 to 9,” says Sylvie Babajko, a biologist from Paris, France. In some parts of the world, as many as 40% of children may have this weakened enamel, she notes. But where it’s been studied well, about 18% are affected.

There are two types of hormones(激素). One is estrogens, known as female sex hormones, and the other one is androgens known as male sex hormones. Both of them control the cells that make tooth enamel.

Over the past few years, Babajko, Katia Jedeon and their team found two pollutants could promote defects in enamel. One chemical was vinclozolin, which can prevent the action of the androgen known as testosterone(睾丸素). But except farm workers, most people don’t meet with this chemical. The other pollutant is BPA, short for bisphenol A, which can affect the action of testosterone. BPA is used to make everything from eyeglasses to kitchen bowls. Some 16,000 different food and drink products use BPA in their packaging.

Kids are most likely to be harmed by BPA very early in life, Babajko says. So for its new study, Babajko’s team exposed pregnant rats to BPA or vinclozolin. Once the babies were born, they were exposed for another month. The researchers then examined cells and their genes in those pups. BPA and vinclozolin both changed a small group of genes, the data show. These genes are directly involved in the enamel-making of teeth. As a result, Babajko now concludes, BPA may be leading to the weakening of enamel quality.

It isn’t yet possible to know for sure if BPA is responsible for weakened tooth enamel. But scientists say there is enough evidence to make further research important.