Look out, Viagra! Your long stint of unrivaled success may come up against a new competitor in a few years. What's behind this new threat to the mighty blue pill? The malodorous (some may say nauseating) gas, hydrogen sulfide. That's the substance responsible for the stench of flatulence, rotten eggs and car exhaust, the unpleasant smell that makes us scrunch up our noses and 10-year-old boys curl over with laughter.

This doesn't mean anyone should bottle up the fumes and take a big whiff before engaging in a lovemaking session. But the discovery that the gas plays a role in promoting male erections could lead to the development of a new anti-impotence drug that would either deliver hydrogen sulfide or enhance the body's production of it.

When researchers at the University of Naples Federico II, led by Professor Giuseppe Cirino, injected hydrogen sulfide into the discarded penile tissue of eight men who had male-to-female sex-change operations, as well as into rats, they found that the gas released certain tissue around blood vessels which allowed more blood to flow, reports the BBC. A study reporting the findings appears in the journal Proceedings of The National Academy of Sciences.

According to WebMD, Viagra and other drugs used to treat erectile dysfunction work by boosting the effects of nitric oxide, which is, like hydrogen sulfide, a vasodilator, meaning it expands blood vessels thereby allowing blood to flow more freely. As a result of increased blood flow, the penis swells in an erection.

This is hopeful news for the one third of men with erectile dysfunction who do not respond to Viagra.