Time to smell the roses in race of life

| Dr. Melody Leung 3 Jul 2019

Dr Melody Leung, Lecturer, Division of Life Science, HKUST

Humans are creatures who often judge whether a dish is attractive or a stranger is friendly simply by their own eyes. But our sense of smell is just as important.

We all may have the experience of eating with a stuffy nose and found a dish to be tasteless or using our nose to check whether it has gone bad.

Moreover, people tend to keep their distance from a person with an unpleasant odor, while special odors like gas can alert us to dangers of a leak.

As the old Chinese adage goes, "My shack is better than an emperor's bed."

What makes our own shack better?

Our smell, together with the smell of our family members, and pets as well if any, makes it unique and reassuring.

To understand how smell impacts people, researchers at the University of British Columbia, Canada, invited 96 couples for a study last year.

Each man was asked to wear a T-shirt for 24 hours without using any scented product and then return it to the researchers in a sealed plastic bag.

Each woman was then randomly assigned to sniff one of the T-shirts and sat for a mock interview, during which her saliva was collected and the amount of stress hormones levels was analyzed.

The study found women who sniffed their partner's T-shirt and recognized the smell correctly, compared with those who sniffed a stranger's or a clean T-shirt, were more relaxed, and their stress hormones stayed at lower levels.

And those who failed to recognize their partner's smell still found the smell somewhat stress-relieving.

This experiment proves that the body's natural scent can, intentionally or unintentionally, trigger our physical and emotional reactions.

Apart from couples, body odor can also enhance the bond between a mother and her baby.

In 2013, using brain scans, the University of Pennsylvania observed that when mothers who had just given birth smelled a newborn baby, the reward system in their brains, which associates with positive emotions such as pleasure, kicks in immediately even if the smell was not from their own baby.

In contrast, women of a similar age but had never given birth found the smells of babies pleasing, but their brain didn't have such a reward response.

As our sense of smell is such a vital part of our lives, how far exactly can our sense of smell go?

Humans have about 400 types of olfactory receptors with each receptor receiving a specific type of particles; and a smell is a mixture of different particles.

In 2014, researchers at the Rockefeller University in New York specified 128 odor particles from which 10 to 30 kinds were extracted for mixture.

They found that as long as the mixture had a difference of more than 50 percent, most testers could distinguish it.

The greater the difference, the easier the detection.

According to statistical calculations, there are as many as one trillion possible mixtures showing a difference of more than 50 percent in composition!

Oh yes, scientists believe the human nose can detect a trillion smells and most of our smell capacity have just not been exercised.

HKUST experts have their fingers on the pulse of a new age of science, technology and innovation

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