The Scent of White
White light is a mixture of all visible wavelengths, and white noise is a combination of all audible frequencies. Following this logic, researchers at the Weizmann Institute of Science questioned if an "olfactory white" could exist. The concept requires a stimulus to meet two conditions: the mixture must span the full range of perception, and each component must have the same intensity. For years, the technical challenge of precisely equalizing the intensity of different scents made this question difficult to answer.
A research team in the Department of Neurobiology, led by Professor Noam Sobel, took on the problem. The group, including research student Tali Weiss and Dr. Kobi Snitz, started with 86 different pure scents, each composed of a single type of molecule, selected to cover the entire "smell map." They carefully diluted each one to achieve a similar intensity before creating various blends. When human volunteers were asked to compare pairs of these complex mixtures, a clear pattern emerged. The more distinct odors a blend contained, the more similar it smelled to other blends, even when they shared no common ingredients. Mixtures containing around 30 or more different odors were perceived as nearly identical.
A Neutral Smell Called Laurax
To test the concept of a generic "white" odor, the researchers gave this new class of smell a nonsense name: Laurax. In one experiment, they created four different fragrances, each made from a unique combination of 40 odor molecules, and labeled each one "Laurax." After participants became familiar with one of the Laurax mixtures over several days, they were presented with new blends they had never smelled before.
The results were consistent. Participants readily applied the name "Laurax" to new mixtures, but only if those blends also contained 30 or more components spanning the olfactory map. Mixtures with 20 or fewer scents were not identified as Laurax. This confirmed the existence of a perceptual phenomenon—olfactory white. When asked to describe Laurax, volunteers found it to be neutral, neutral. The finding suggests that the brain’s olfactory system perceives complex scents as a whole, averaging the components into a single perception rather than analyzing each molecule individually.