Light of all colors or wavelengths combines to form white light. Similarly, sounds of all different frequencies mix to produce white noise. A group of scientists from the Weizmann Institute of Science in Israel decided to find out whether this phenomenon applied to smell as well.
The researchers discovered that a white odor does, in fact, exist. They described how they arrived at the indescribably bland scent, which they coined “olfactory white,” in an article published in the journal Proceedings of the National Academy of Sciences on Nov. 19.
The scientists chose 86 different odor molecules, diluted them to the same intensity and then combined them to create mixtures, each with between one and 43 molecular components. Human participants first compared mixtures containing the same number of elements (but including none of the same components), which revealed that people had more trouble telling mixtures with more ingredients apart than those with less elements.
“The more components two mixtures have, the more similar they smell, even though they have no individual components in common.” the researchers wrote in the paper. “With ~30 components, most mixtures smelled alike.”
The results of the comparison test led the study’s authors to design another experiment, in which they developed four different 40-element mixtures and labeled them with the nonsensical name “Laurax.” For three days, 12 participants smelled the mixtures, with three participants assigned to each one. On the fourth day of the test, individuals had to apply four labels — one of which said “Laurax” — to new scents. The scientists discovered participants were more likely to classify mixtures as “Laurax” if they contained more compounds, with odors comprised of more than 40 elements receiving the label 57.1% of the time.
Another experiment repeated the test, except this time, researchers provided the additional category of “other” to control for participants’ potential use of “Laurax” as a catch-all. Mixtures with more components continued to be more likely to receive the label “Laurax.”
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The results confirmed to the scientists that they had created “olfactory white,” which arises when numerous elements of the same intensity that span the range of human scents combine. The number of components and their intensities, rather than their identities, play a crucial role in determining whether a smell is white.
This explains humans why can identify aromas such as coffee, LiveScience reported. Although coffee comprises a myriad of compounds, its components are unequal in intensity and fail to span the range of scent, allowing it to be distinguished from other smells such as roses, and of course, “olfactory white.”
Unfortunately, chances of getting a whiff of the white odor are slim. Although the researchers wrote that the “best way to appreciate the qualities of olfactory white is to smell it,” they believe the scent’s existence in nature “would constitute an extremely rare event,” similar to the rarity of naturally occurring white noise and light. Even explaining the odor is a nearly impossible feat, with participants using 146 different words to describe the smell and characterizing it as “largely intermediate” on key aspects of olfactory perception — edibility and pleasantness.
“This variability can be taken to imply that white does not smell like any particular common object,” the study’s authors wrote.
Despite its nondescript qualities, the Weizmann Institute scientists hope that “olfactory white” can help further research in the same manner as its auditory and visual counterparts.
“Both white light and white noise also are rare in nature, but they have served significantly in the neurobiological study of vision and audition,” they wrote. “We hope olfactory white can serve similarly in the study of olfaction.”