From: Andy Soos, ENN
Published April 21, 2010 01:23 PM

Smells and Aging

Smell is one of the five senses. It is how we interact with the world. What does the smell of a good meal mean to you? What are good smells and what are bad smells? Are there effects beyond just being pleasant or unpleasant? Specific odors that represent food or indicate danger may be capable of altering an animal's lifespan and physiological profile by activating a small number of highly specialized sensory neurons, researchers at the University of Michigan, University of Houston, and Baylor College of Medicine have shown in a study publishing by the end of April in the online, open-access journal PLoS Biology.


Olfaction is the sense of smell. It consists of the main olfactory system, and the accessory olfactory system (mainly used to detect pheromones).  Olfaction is a form of chemoreception. The chemicals themselves which activate the olfactory system, generally at very low concentrations, are called odorants.

Humans have about 1.6 square inches of olfactory epithelium, whereas some dogs have 26 square inches). A dog's olfactory epithelium is also considerably more densely concentrated.  Hence this is one reason why dogs are more sensitive to odors and smells.

Humans smell these odors through the nose. As you breathe in, the air enters through your nostrils. After passing through the nasal cavity, the air passes through a thick layer of mucous to the olfactory bulb. There the smells are recognized because each smell molecule fits into a nerve cell like a lock and key. Then the cells send signals along your olfactory nerve to the brain. At the brain, they are interpreted as those sweet smelling flowers or that moldy cheese or whatever the smell is.

For humans the sense of smell is connected to our memory. For instance, the smell of popcorn can remind you of being at the movies with a friend or the smell of tar can remind you of riding in a car to the beach.

Humans have seven primary odors that help them determine objects. Listed below are some common odors.

Camphoric (such as mothballs)

Musky (such as perfume)         






If your nose is at its best, you can tell the difference between 4000-10,000 smells!  As you get older, your sense of smell gets worse. Children are more likely to have a better sense of smell than their parents or grandparents.

Some recent research in various organisms and in humans has shown that sensory experiences can potentially impact a wide range of health related characteristics including athletic performance, type II diabetes, and aging. Nematode worms and fruit flies that were robbed of their ability to smell or taste, for example, lived substantially longer. 

Using molecular genetics in combination with behavioral and environmental manipulations, collaboration between the laboratories of Scott Pletcher and Gregg Roman has succeeded in identifying carbon dioxide (CO2) as the first well defined odorant capable of altering physiology and affecting aging in some organisms.

Flies incapable of smelling CO2 lived longer than flies with normal olfactory capabilities. They are also more resistant to stress and have increased body fat. To many insects, including fruit flies, CO2 represents an ecologically important odor cue that indicates the presence of food (e.g. rotting fruit or animal blood) or neighbors in distress (it has been implicated as a stress pheromone). Indeed, this set of research has previously showed that merely sensing one's normal food source is capable of reversing the health and longevity benefits that are associated with a low calorie diet.  CO2 seems to be responsible for this effect.

"We are working hard to understand how sensory perception affects health, and our new result really narrows the playing field. Somehow these 50 or so neurons, whose primary job it is to sense CO2, are capable of instigating changes that accelerate aging throughout the organism," says Scott Pletcher.

Sensory perception has been shown to impact aging in species that are separated by millions of years of evolution, suggesting that similar effects may be seen in humans. "For us, it may not be the smell of yeast, for example, or the sensing of CO2 that affects how long we live, but it may be the perception of food or danger," says Pletcher. If so, a clever program of controlled perceptual experience might form the basis of a simple yet powerful program of disease prevention and healthy again

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