Listen carefully, though, and he often turns to debates that transcend his day-to-day work, escaping entirely from the realm of science and drifting into the metaphysical: Is human aversion to tainted odors nature, or nurture, or both? How can one measure a perception? And how do you give people the confidence in their nose that they have in their eyes and ears?
What the nose can tell us
An odor is simply the result of chemicals in the air, and the human nose is much better at detecting it than it often takes credit for. Some of the most recognizable and powerful odors, such as hydrogen sulfide (think rotten eggs), can be detected at even the smallest concentrations, such as 1 part per billion.
“If you mapped the distance from New York to Los Angeles, 1 part per billion would represent just a few centimeters along that route,” said Dr. Koziel of the State of Iowa.
That fact also reflects how difficult it is to regulate odors. At such vanishingly small concentrations, hydrogen sulfide is unlikely to pose a health risk. Nevertheless, “it is very disturbing to people,” says Susan Schiffman, a clinical psychologist who has studied smell and taste for half a century.
Despite having the power to get sick, there are few laws in the United States to regulate odor. It makes up a significant proportion of complaints to public authorities, including a quarter of complaints to the federal Agency for Toxic Substances and Disease Registry. Still, there is debate as to whether a fragrance can be inherently dangerous.
“Measuring emissions is one thing, but smell is a sensation. Because it can be experienced so differently by so many people, it makes us insecure about how we regulate,” said Pamela Dalton, a psychologist who studies odor perception at the Monell Chemical Senses Center in Philadelphia. “Every industry has the potential for external emissions, even a biscuit factory,” she added.