Washington:  A hormonal gel combo applied daily to the skin showed promise as a male contraceptive by reducing sperm production, say U.S scientists.

About 89 percent of men using the new combo of skin gels enriched with testosterone and a new synthetic progestin called Nestorone, reported very low sperm counts.

"This is the first time that testosterone and Nestorone have been applied to the skin together to deliver adequate amounts of hormones that suppress sperm production," said principal investigator Christine Wang, professor at the University of California's Los Angeles Biomedical Research Institute.

"Men can use transdermal (skin) gels at home - unlike the usual injections and implants, which must be given in a health care provider's office," added Wang, according to a California statement.

Prior studies of male contraceptives that combined testosterone and progestin used progestin pills, implants or shots, according to Wang.

In men, progestin increases the contraceptive effectiveness of testosterone.

Both testosterone and progestin work together to turn off production of reproductive hormones controlling the production of sperm, she said.

Wang added that unlike other progestins studied as male contraceptives, Nestorone has no androgenic (male hormone) activity. Androgenic activity may cause side-effects such as acne and changes in good and bad cholesterol.

"The combination of testosterone with Nestorone had few adverse effects," Wang said. "It warrants further study as a male contraceptive."

Nestorone is an investigational new drug being developed by the Population Council, a non-profit organisation in New York City, which supplied this drug for the study.

These findings will be presented Sunday at the Endocrine Society's 94th annual meeting in Houston, U.S.