Ask a RIFM Scientist: If I Can Smell It, Is It Safe?



Last week, the New York Times asked the question What’s the World’s Worst Smell? The riveting article opens with an introduction to Monell Chemical Senses Center’s Pamela Dalton, whose experiments on bad smell led her to discover that people don’t always agree on whether a particular odor is good or bad.

The article also points out a common misunderstanding: if you can smell it, there must be a lot of it. Our perception of odor is so sensitive that it often takes very little of a substance—imagine a single drop of ink in a large tanker truck—to deliver a sharp, lasting note that tricks the brain into believing there’s a lot more of the molecule than there is.

The Times article gives the example of vanillin, a widely used fragrance chemical derived from vanilla beans, which is so scent-strong that “one or two oil tankers full of vanillin … [might be] powerful enough to give the entire Earth a slight scent of vanilla.” (Discover vanillin on the Fragrance Conservatory website.)

Studying the Odor Threshold for Fragrance

Nikaeta SadekarThe Research Institute for Fragrance Materials (RIFM) is currently working on establishing a research project to study odor thresholds in humans. Leading the project is RIFM’s Senior Associate Scientist of Respiratory Toxicology, Nikaeta Sadekar, PhD.

Q: What do we know about the odor thresholds of fragrance materials?
A: Odor thresholds are the lowest concentration levels at which a person can detect a smell in their immediate environment. Smells or odors are a part of the physical-chemical properties of a material. RIFM has compiled many earlier studies that looked at odor thresholds in humans, but the current science has replaced the techniques and study designs used at that time with more sophisticated, refined versions. So, what we know is not necessarily current. 

Q: How would you address the notion that, if a person can smell something, there is enough of it to be harmful?
A: A smell can have a strong emotional or psychological effect, and depending on the exposure, there can also be a physiological effect. But as a toxicologist, I would quote Paracelsus: “The dose makes the poison.” 

In some cases, humans can smell and detect odors in parts per billion, much lower than the existing inhalation exposure reports we have on some fragrance materials. These reports show that it takes an exposure well above the odor threshold to manifest into any physiological effect, such as irritation.

Q: What is RIFM hoping to achieve from this research?
A: RIFM’s database houses total chronic inhalation exposures from the highest users of fragranced products, and even these high-end user exposures are very low. 

We hope that scientifically measuring the odor thresholds will further our knowledge of how strong-smelling these fragrance materials can be. Learning about odor thresholds, in turn, may help consumers make better decisions about the products they are using in their daily routines. (Read more about this and other RIFM research projects in RIFM’s 53rd Annual Meeting brochure.)