When the term "pheromone" was defined in the late 1950s by insect researchers Peter Karlson and Martin Lüscher, it carried three main implications: that it was a message to which only members of the same species would respond; that it was a single, identifiable chemical; and that it had a definite behavioral or physiological effect on the recipient.
That definition has not held up well over time. Even in insects, each of the criteria has been violated by substances that most researchers are still willing to call pheromones. For vertebrates, the definition has been progressively loosened to the point that researchers are now heatedly debating the meaning of the term. Scientists now suggest there are four kinds of human pheromones--primers, releasers, modulators and "signalers" that provide information to the recipient without directly altering behavior.
Some researchers, such as Richard Doty, PhD, editor of the Handbook of Olfaction and Gustation and a professor at the University of Pennsylvania, believe the term should be used only in the narrowest sense--in part because those who use looser definitions can label and sell almost anything as a pheromone.
"In 50 years, nobody's really identified a [mammalian] pheromone that will hold up to any sort of criteria, with the exception of maybe one or two," he argues. "My view is that the whole thing is primarily driven by the perfume industry, and when looked at carefully sort of falls apart."
Meredith, Sobel and others are more sanguine about the existence of human pheromones, but all agree that the research community and the public would both benefit greatly from a common definition. "The word is not going to go away, so better to define it than ignore it," says Michael Meredith, PhD, of Florida State University.