Scientists believe a type of chemical found in children's plastic toys may make men less fertile.
A study of 501 couples found exposure could lead to a 20 per cent dip in male fertility.
The substance - called phthalate - is also in tablet coatings, PVC, glue, packaging and food products.
Couples in Texas, were tested for levels of phthalate and another chemical, Bisphenol A or BPA, used in water bottles, and DVDs.
They also kept journals on intercourse and lifestyle and the women recorded their menstrual cycles and pregnancy test results.
The results showed the higher BPA concentrations found in the female partner did not lead to decreased fertility, although previous studies have linked it with a higher risk of miscarriage.
Dr Linda Giudice, of the American Society for Reproductive Medicine, said: "The chemicals are a cause for concern."