Apparently, the spiciest concoctions are the hottest means to pain relief.

A team of Harvard researchers has found that the chemical that makes chili peppers hot combined with a particular anesthetic can diminish pain in rats without any of the negative side effects seen in other pain killers.

“It started off as an idea. I thought it might work, but I wasn’t sure,” said Bruce P. Bean ’73, a professor of neurobiology at Harvard Medical School. His team published its findings in Nature yesterday.

The mechanism behind their discovery is that the spicy chemical, capsaicin, binds to certain receptors, which are found only on pain-sensing neurons.

This binding allows the anesthetic, QX-314, which is unusual in that it cannot ordinarily enter the cell on its own, to enter nerve cells.

Through this mechanism, the anesthetic can affect pain-sensing neurons exclusively but effectively.

On the other hand, conventional local anesthetics have the drawback of working on all neurons, including those responsible for touch and movement, sometimes causing numbness and paralysis.

“The new principle of opening a channel to deliver the agent is a new and very promising development,” said Igor Kissin, professor of anesthesia at Harvard Medical School.

Bean said that there is much work ahead for him and his colleagues.

“It would be most exciting if we can work the same concept in humans,” said Bean, adding that he immediately thought of childbirth as a possible application.

Bean said that the capsaicin, despite being intended as an anesthetic, probably caused the rats extreme pain in the short term, although its pain-numbing effects last up to three hours.

“When injected or even put on the skin, the pain of capsaicin is quite intense,” said Alexander M. Binshtok, a post doctoral fellow at the Medical School who worked on the study.

The team is now looking to make compounds with similar though less painful effects. Clifford J. Woolf, a professor of anesthesia research at Harvard Medical School, was also a key contributor to the study.

“While we can’t predict what will happen with humans, we hope it will have similar results to rats,” Binshtok said.

Kissin said he is optimistic.

“Although the clinical possibilities will require additional work, it is quite possible that this principle will also be possible in humans one day,” he said.

—Staff writer Christina G. Vangelakos can be reached at cvangel@fas.harvard.