Let me start by relating a common occurrence in my home.  The scene begins with my son and me home alone.  Then my wife and daughter arrive, open the door, screw up their faces in looks of disgust and announce loudly, “Dear God what is that smell!?”  My son and I exchange looks of confusion.   For this week’s column I decided to delve into the science behind this scene.
Let’s start with the mechanics of smelling.  In order for you to smell something it must release volatile chemicals which float through the air and enter your nose.  In the upper part of your nasal cavity is an area known as the olfactory epithelium which has receptors designed to sense the chemicals.  The receptors send specific electric signals through your nerves to your brain based on the structures of the chemicals. Your brain’s reaction to this electrical signal is the “smell”. It may surprise you to know that the details of the biophysics of smell are still a matter of academic study.  In fact, as recently as 2004 the Nobel Prize for Physiology and Medicine was given for studies of smell. 
The part of the brain which processes smell is closely associated with emotion. As a consequence, smells can help to trigger memories, even those from childhood, and be a factor in selection of consumer products, a fact well known by marketing departments.  Smell is also an important factor is the selection of husbands.  I purposely chose the word husband rather than spouse.
The superiority of the female gender’s sense of smell is not an urban myth.  Women can sense the presence of odors at much lower concentrations than men and they are much better than men in identifying smells.  However, women’s sensitivity to smells is not uniform; there are some items their olfactory epitheliums are more highly attuned to than others. For example, women’s noses are more sensitive to male body odor than female body odor. As a result, mothers around the world are much more likely to send their sons to the shower rather than their daughters. (Though gender based differences in hygiene practices may also play a role here.)  Evolutionary scientists believe that the sensitivity to male body odor arose from women’s noses guiding them towards mates more likely to be successful in reproducing.
The reasons why women’s noses work better than men’s are not fully understood.  Women do not have larger olfactory epitheliums or more chemical receptors in their noses compared to men.  The prevailing theory is that women’s heightened sense of smell stems from collaboration between the chemical receptors and their hormones.  This view is strengthened by the fact that women’s sense of smell is even more acute during pregnancy, a time of increased hormonal activity.
So the conclusion of this week’s column is somewhat incomplete.  We know that women’s sense of smell is better than men’s and that it is likely hormonal in origin but the detailed mechanism is unclear.  As I have mentioned in the past, I enjoy situations where familiar aspects of life, like odor or gravity, still retain elements of mystery.  I’ll close this week’s column with a brief personal confession.  When my wife and daughter are remarking on the offending odors they encounter, I am not jealous of their superior olfactory function.  Rather, I’m grateful for my shortcomings.
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