Historically, our sense of smell helped our ancestors find food and avoid predators, as well as seek receptive mates. But the sense of smell is important today too. Without a sense of smell, food wouldn’t taste the same to you and there’d be no reason to wear perfume, and that’s just the beginning.
Smell is one of the chemical senses. Taste is the other, and often smell and taste work together. Odours are sensed by chemoreceptors that react to specific chemicals in food and air. The receptors are known as olfactory cells, and the complete system is sometimes called the olfactory gland. While people have their olfactory glands in their noses, insects have theirs on their antenna.
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The olfactory cells are located in about a one-inch square area, high on the roof of the nasal passages. These cells are actually specialized endings of fibres that make up the olfactory nerve, like the end of a fraying rope. Each cell ends in a tuft of six to eight cilia, and it is on the cilia that the molecules of the chemicals bind.
Once the chemical and receptor are bound together, the cilia and molecules generate a nerve impulse which is sent along the olfactory nerve and interpreted by the brain as a specific smell.
There are about 1,000 varieties of olfactory cells, and you may have up to 50 million of them. The cells have a lifespan of about two months, and when they die they usually are replaced.
Unfortunately, as you age the number declines and about 15 per cent of seniors have anosmia, meaning they have no sense of smell. This lack of smelling ability can be a problem if spoiled food is eaten.
It is the combination of odour molecules that bind with the receptors that produces the variety in smells. This is why, when you inhale the same perfume, you may perceive the scent of roses, but someone else may notice lilacs.
And, because the sense-of-smell centre in the brain is adjacent to your memory centre, specific smells may be so strongly linked to specific memories. For example, the smell of baking bread may remind you of your childhood and Saturday mornings in the kitchen with your mother.
Head or nose trauma can damage either the interpretation or the sensing of a smell. Environmental pollutants, workplace chemicals, and even smoking can damage the olfactory cells. However, if the damage is not serious, the sense of smell may return.
Malnutrition can diminish your sense of smell, and anything that blocks air flow through the nasal passages impairs it, for example a cold with blocked nasal passages, or nasal polyps. People with Alzheimer’s disease or Parkinson’s disease seem to have diminished ability to sense smells as well, but it isn’t known if the effect is due to changes within the brain.
Drugs can impact smell. Steroids that are used to treat inflammation can reduce the number of receptors and the ability to smell. Chronic use of decongestants dries up nasal passages, thereby reducing the mechanism of smelling. Radiation therapy, estrogen supplements, and amphetamine drugs including those used illicitly all alter the sense of smell.
Zinc, a mineral found in many multivitamin/ mineral combinations, seems to affect smell for some people. Luckily, the damage to smell is usually not permanent and once the drug is stopped, smell returns.
You can improve your sense of smell by exposing it to a variety of odours. However, you may not develop the sensitivity of people who work for instance as perfume testers and use their noses to professionally test odours.
Also remember that taste is closely linked with smell, so if you don’t like the taste of a food, hold your nose. You won’t smell the food, and the taste will be less noticeable. What the chef will think of you, however, is another consideration altogether.
Marie Berry is a lawyer/pharmacist interested in health care and education.
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This one square inch of olfactory nerve endings makes pleasure, and pain
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