US scientists have found long sought proof that people release potent chemical signals that can have profound effects on other people. The research settles a 40 year debate about whether humans produce and can respond to "pheromones," molecules that are usually airborne and odorless and that influence, in other species, mate choice, the recognistion of one's own family members and the ability to "smell" the difference between friend and foe. The finding may also lead to the discovery of compounds in sweat that could be incoporated into fragrances to alter body chemistry or mood.