MadSci Network: General Biology
Query:

Re: Why does perfume smell differently on differnt people?

Date: Mon Nov 26 10:46:08 2001
Posted By: Jurgen Ziesmann, Post-doc Biology and Ecological Chemistry, U. Maryland Medical School
Area of science: General Biology
ID: 1005286059.Gb
Message:

Dear Whitney

Thank you for your very interesting question, why one and the same perfume 
smells differently on different people. 

A one sentence answer is: because the skin is different.

That is not a very satisfying answer, so let me try to explain. You could 
even do a science project on this if you have access to a very accurate 
scale (in the millligram area).

Imagine (or do it as an experiment), you put a small amount of a odorous 
chemical on  a piece of glass and then on the scale. What will happen? The 
amount of chemical on the glass will get less and less over time until it 
finally will be gone completely - it evaporates and the scale can tell you 
the rate of evaporation.
Now imagine, you try a different chemical. In principle the same will 
happen, but most certainly one of the chemicals takes longer time to 
evaporate.
Now mix the two and repeat. The result will be a mix inbetween the two. If 
you use your nose, in the beginning you will smell the chemical that 
dissapears more quickly as dominant, later the other one. This happens also 
every time with a perfume that are usually complex mixtures of 20 and more 
chemicals.
 
The "top note" is the first fragrance you get when you smell the perfume. 
The "middle note" can be smelt after wearing the perfume for a while, so 
that it dries on your skin and begins to mix with individual body chemistry. 
The "base note" is the fragrance which lingers. It begins to emerge about 
twenty minutes after application. 

Now back to the experiments. 
1) Imagine you repeat the three experiments but you heat the glass by 10 
degree Celsius. What happens? The odorants evaporate more quickly, but 
different chemicals are slightly differently affected. 
2) Imagine you wet the glass with water before applying the chemicals. The 
chemical that dissolves better in water now takes much longer to dissapear.
3) Imagine you cover the glass with a fine layer of fat or oil. The chemical 
that dissolves better in oil now takes longer to evaporate.
4) Imagine you cover the glass with collagen powder, one of the components 
of skin. The better the chemical binds to this collagen, the slower it 
evaporates.

You probably can imagine that skin is a very complex mixture of chemicals. 
You have water and fat, fatty acids, salts, sugars, proteins, fibers, and 
hairs. (You probably have heared about different skin types like dry skin, 
fatty skin, mixed skin.) Each of the components of skin binds the chemicals 
in the perfume differently and will release it differently. So different 
composition of skin make the single components of the perfume evaporate more 
slowly or quickly. Because everybody as a unique skin (if you look exacly 
enough) for everybody the mixture and amounts of chemicals released is more 
or less different. 
These differences are detectable by our nose  the perfume smells 
differently.

That is inprinciple the answer, but it does not even stop here. Change the 
amount of chemical you apply, for example 2 fold, 5 fold, 10 fold. Or repeat 
the experiments but cover the glass by one sheet of fabric. Compare the 
evaproation rates you get on a day with high and low humidity. And finally: 
the background odors: every room smells different, in a forest the 
background is different compared to the backyard, to a restaurant, to a 
shop, to the cinema. These background odorants change the way our receptor 
cells in the nose respond to chemicals.

You see, it is quite difficult to predict the outcome of the simple 
experiment: we put perfume on skin - what happens? 

I hope my answer helps.
If you have more of these interesting questions plese come back soon.

You need more information? 
Try this pdf file on 
problems in flavour research.
Or go here for 
information on olfaciton, the sense of smell


Jurgen Ziesmann



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