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Puzzling Facts about Olfaction

for full article see: Perfumer & Flavorist, Vol. 26, Jan/Feb 2001
with additions by Jeanne Rose

Language is important in recognizing smells.  An important part of perfumery training is to develop an odor language based on olfactory standards.  The possession of such an odor language increases the powers of discrimination.  Start with the Jeanne Rose Basic 7  Vocabulary of Odor.

Different people perceive odors differently. Smell is subjective and it is easily demonstrated that, at least in some cases, we do not all perceive the same material in the same way. This is why education/vocabulary is the key to be able to describe odors through a group of people,

Perception of odors can be distorted. Psychological pre-conditioning can distort the perception of the odor.  For example, a fragrance chemist can be affected by seeing the structure of a molecule before smelling a sample and a wine expert by the addition of an odorless and tasteless red dye to a white wine or even by the bottle from which the wine is poured.

Can't smell a pure sample but know it in something else. Some people may be unable to smell a specific material when presented with a pure sample, yet will be able to recognize its presence in a fragrance.

Can't smell certain odors. Some individuals are anosmic to an odor type, for example there are individuals who cannot smell any musk materials.  But it is very common, possibly universal, that an individual will be unable to smell one representative material of a given odor class yet will perceive other materials of the same class very strongly (as an example to illustrate this point and the one immediately preceding it, there is a perfumer who can smell all musks except galaxolide, yet can easily recognize if galaxolide  is present in a fragrance.)

Olfactory illusion. In some cases, a perfumer can identify by smell alone all the components of a fragrance, even if some of these components are themselves complex mixtures, such as essential oils.  However, in other cases, blending of ingredients can create the illusion that a certain material or class of material is present when it is not.  In other words, it is possible to create an olfactory illusion.  In the first case, the sense of smell appears to provide us with an extremely effective analytical device, yet the second case shows that it can be deceived. 

People can be trained to smell odors. People can sometimes learn to smell materials to which they were previously anosmic. Take a sample, label it, look at it and smell it several times daily and say the name of the sample while smelling.  Do a different odor every month or as you learn the previous one.

Similarly molecules, different odors. There are many examples of cases where two very similar molecules elicit very different odors, yet a third molecule which apparently bears little structural resemblance to either of the first two, elicits an odor very similar to one of them.

Function and shape matter. Sometimes a specific chemical function seems to be crucial in producing a specific odor, for example, the association of the ester function with pear.  In other cases, the molecular size and shape are much more important then chemical function, for example in the case of the camphor odor, a hydrophobic ellipsoidal shape of the correct size is all that seems to matter. Vibration matters.

Keys of Scent fit into the sensory locks of odor in the nasal mucosa (in the same way that your house keys fit correctly into your house locks).

All Rights Reserved 2003, 2004. No part of this article may be used
without prior permission from The Aromatic Plant Project.
Author's Copyright and Jeanne Rose,

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