What's that Smell?

Weizmann Institute scientists have created a “white smell.” Think about white light or white noise: Each mixes a bunch of different waves together from various parts of the visual or audible spectrum. Those wavelengths combine such that we perceive that unobtrusive light or sound we call “white.”

How do smells fit into this scenario? Prof. Noam Sobel and his group have already shown that smells have their own spectrum – ranging from pleasant to unpleasant – and that this relates to the chemical structure of the odor molecules. Is this spectrum truly analogous to that of light or sound? That is, can one take bits from different parts of that spectrum, mix them together and come up with a convergent stimulus?

It turns out that if you take enough different and varied scents – at least 30 – dilute them all to the close to the same intensity and mix them together, you can produce a white smell. That is, those who smell it will perceive it to be neither pleasant nor unpleasant. And like white light or white sound, the exact mix doesn’t really matter, as long as the range is large enough and the intensities similar. The research team mixed up various versions of the odor blend and, past 30 different scents, the subjects who smelled them thought they smelled the same.

Aside from possible applications in the odor neutralization industry, the findings, says Sobel, reveal something very fundamental about our sense of smell. According to him, the smells we perceive are more than just the sensations from a lot of different smell receptors added together -- but it turns out they can also be less. As in vision and hearing, the mechanical receptors in our sense organs are tuned to specific stimuli, but when all of those stimuli come together, the sum of our perception can be simply “white.”