We are fascinated by our sense of taste and smell.  Our sense of smell accounts for about 90% of what we taste. The tongue handles just 10%: sweet, sour, salty, bitter and umami. More on this at http://en.wikibooks.org/wiki/Human_Physiology/Senses .

The olfactory organ and perhaps our second olfactory organ, Jacobsen’s organ, located in our noses and faces do the rest. Aroma preferences are learned. Put another way, our sense of smell is adaptive, meaning we learn by experience whether a smell is good or bad, healthy or unhealthy, pleasant or repugnant.

Olfactory nerves go straight to oldest part of the brain, the so called reptile brain or rhinencephalon, right in the center of your head. This is adjacent to the limbic system, where memories and emotions are located. Particular smells can bring back specific memories and a flood of emotions, and this is of particular interest to us as wine tasters. While sight, sound, and feel are all memory cues, smell triggers much larger emotional responses than the other senses. Olfactory receptors live about eight weeks and new ones take their place. More on this at http://nobelprize.org/nobel_prizes/medicine/laureates/2004/press.html .

While most people rate  the loss of smell to be only as important as losing a big toe, the reality can be quite different. Loss of smell is associated with a loss of interest in normally pleasurable pursuits, feelings of sadness, loss of appetite, difficulty sleeping, loss of motivation, inability to concentrate, and thoughts of suicide that can lead to action if not treated.

Humans have about 20 million olfactory receptors, bloodhounds have 220 million.  Bloodhounds and bees can all be trained to sniff out things. Salmon have such a keen sense of smell they can find their way back to the waters of their birth from the open ocean.

Odors can be used to re-inforce positive or negative experiences, and odors can trigger Post traumatic Stress Disorder.

People given an almost impossible test were subjected to an unfamiliar scent. They found the test to be extremely frustrating and did poorly. Next the group was split up into three groups, one with the unfamiliar scent, another with another unfamiliar scent, and the other in an odor free room,  and given another difficult test. The group exposed to the first scent room scored lower than the other two groups, who did better.

We’ve all had the experience of having eaten something just before getting the flu and visiting Ralph on the big white phone, and having a lasting negative reaction to that food for quite a long time, if not forever. Post traumatic stress may be triggered by a smell if  people have been in a traumatic situation like an assault where there was a characteristic smell associated with it. Therapists treat people with this problem by desensitizing people to the stimulus.

People are easily deceived by the power of suggestion.  The same scents can either be labeled relaxing or stimulating, both with positive results. Scents can hijack our minds and bodies through emotional associations.

Body chemistry: There are 50 closely connected genes on the same chromosomes called the Major Histocompatability Complex (MHC). Each person has a unique set. The genotype for this our immune system, and its outward manifestation, the phenotype is our unique body odor.

What is interesting about this is people tend to pick mates who smell differently than they do. This causes them to pick mates with different immune systems which make for healthy offspring.  Women who take the pill tend to pick mates with similar smells because the pill mimics pregnancy and women tend to surround themselves with family members who smell like them to protect them. It has been conjectured that this may be the reason why 50% of modern marriages end in divorce. More on this at http://en.wikipedia.org/wiki/Major_histocompatibility_complex .

Jacobsen’s organ, which is our second olfactory organ, is responsible for processing larger non volatile molecules oftentimes associated with sex, like  pheromones. Jacobsens organ is located in the nose and behind the front teeth. It is present in most humans and vertebrates  though there is much conjecture as to whether it functions in humans. More on this at http://chemistry.about.com/cs/medical/a/aa051601a.htm .

Babies know the smell of their mothers because they smell very similar to themselves. One of the first things a baby learns is the smell of the womb. An easy way to quiet a baby down is to give them a piece of clothing which the mother has worn. Mothers can easily identify their own children buy their sense of smell.

Odor adaptation: We easily become accustomed to the ambient smell of our immediate environment. Bejing, China lost its bid for the 2004 Olympics because the city smelled of public latrines, yet the smell didn’t seem to bother the citizens of that great city. In India the odor of burning bodies is quite common, and it is associated with funeral rites on the banks of the Ganges. When I lived in Germany, I could never get used to the smell of diesel everywhere.

Source books:

The Scent of Desire, Rachel Herz, 2007, Harper Collins.

Smell: The Secret Seducer, Piet Vroon, 1997  Farrar, Straus & Giroux.

Jacobsen’s Organ, Lyall Watson, 2000, W.W. Norton.

What the Nose Knows, Avery Gilbert, 2008, Crown Publishers.