Scientists may have new ways to fight mosquitoes that work works longer than DEET -- the most common method used today -- without an unpleasant smell or sticky sensation, according to a news release from the American Chemical Society.

But researcher Ulrich Bernier said the costly, time-consuming pre-market testing and approval process could keep the new products off the market.

"Clearly, the odds are stacked against new repellent products making it to market," he noted.

Bernier and his team discovered the repellents with what they say is the first successful application of a computer model using the molecular structures of more than 30,000 chemical compounds tested as repellents over the last 60 years.

Using 11 known compounds, they synthesized 23 new ones. Of those, 10 gave about 40 days protection, compared to 17.5 days for DEET, when a soaked cloth was worn by a human volunteer. When applied to the skin, however, DEET lasts about five hours.

Bernier said studies are also evaluating the effectiveness of the repellents against flies and ticks.

"This was quite an ambitious project," Bernier said. "The USDA historical archives and repellents database we used consisted of more than 30,000 chemical structures tested over the past six decades."