The search for smells that can be used against enemy combatants — by making them throw up, become dizzy and possibly flee the battle arena — has become a serious business. Most efforts now under way fall under the aegis of the Defense Department’s obscure Joint Non-Lethal Weapons Program, which began its quest for the ultimate adversarial aroma a few years ago. Now it’s seeing results.

The effort was spearheaded at the Monell Chemical Senses Center, a research institute based in Philadelphia. Pamela Dalton, a resident scientist, rose to the challenge of developing ”psychologically toxic” odors — smells that would cause sniffers to lose their appetites for aggression. But this challenge came with a catch: the military wanted an equal-opportunity odor, something offensive to everyone, everywhere, and not just to members of certain cultural groups.