U.S. researchers said Friday that two sunscreen chemicals used to protect against ultraviolent (UV) rays appear to impair men's ability to father children.

The chemicals, known as Benzophenone-2, or BP-2, and 4OH-BP, respectively, may cause a 30 percent reduction in fecundity, the biological ability to reproduce, the researchers from the National Institutes of Health (NIH) and the New York state Department of Health's Wadsworth Center said.

That's because the chemicals, upon being absorbed by the skin, can interfere with the body's hormones and endocrine system processes.

Lower fecundity may result in a longer time to pregnancy, the researchers reported in the American Journal of Epidemiology.

BP-2 and 4OH-BP belong to the group of compounds called BP-type ultraviolet filters, which comprise a class of about 29 chemicals commonly used in sunscreens and other personal care products to protect skin and hair from sun damage.

The researchers studied 501 couples that were trying to conceive a child, and followed them until pregnancy or up to one year of trying to record the time it took for the women to become pregnant.

They also tested participants' urine samples and measured concentrations of five selected UV filters associated with endocrine-disrupting activity.