A flower smells sweet because of the combined effect of hundreds of odours
A flower smells sweet because of the combined effect of hundreds of odours
A flower smells sweet because of the combined effect of hundreds of odours
A flower smells sweet because of the combined effect of hundreds of odours

The human nose can detect one trillion different odours, far more than we previously thought, say US scientists.

Until now, the long-held belief was that we can sniff out about 10,000 smells.

New estimates published in?Science?suggest the human nose outperforms the eye and the ear in terms of the number of stimuli it can distinguish between.

Researchers at the Rockefeller University say we use only a tiny part of our olfactory powers.

The human eye uses three light receptors that work together to see up to 10 million colours, while the ear can hear almost half a million tones.

Until now it was believed the nose, with its 400 olfactory receptors, could detect only about 10,000 different odours.

Scientists at the Rockefeller University, New York, set out to test the idea, which dates back to 1927 and was never scientifically investigated.

They devised experiments to see how good people are at distinguishing between cocktails of 128 different odour molecules, representing a large range of smells from grass to citrus.

The molecules were mixed randomly in groups of 10, 20 or 30 to create unfamiliar smells.

The 26 people were then asked to identify a scent from three samples – two that were the same and one that was different.

Based on these results, the researchers used theory to extrapolate how many different scents the average person would be able to discriminate if they were presented with all the possible mixtures that could be made from the 128 molecules.

They estimated that the average person can discriminate between at least one trillion different odours with the nose, far more than can be detected by the eye or ear.

This is probably an underestimate, they say.

‘Urban legend’

The conventional wisdom on how well we can smell was based on little more than “urban legend”, said co-author Dr Leslie Vosshall.

“It’s the first real test of how good humans are,” she told the BBC.

“People assume animals are much better smellers than us. Humans are remarkably good at smelling things.”

She said animals remain two or three times better than us at smelling, as they devote more of their brain to the sense of smell.

However, the power of the human sense of smell should not be underestimated.

“You can push the sense of smell to work harder – you can get bigger and crazier, more intense perfumes,” she added. “We are using a tiny part of our olfactory powers.”

According to Charles Spence, professor of experimental biology at the University of Oxford, while it is good to see smell pushed up the rankings of human senses, there is still a lot to learn.

“I guess no matter how many smells we can discriminate, the evidence still shows that even the best experts cannot really pull much more than three odourants out of a mixture, contrary to what all those wordy wine writers might have us believe,” he said.

Prof Stephen Liberles, of the?Department of Cell Biology at Harvard Medical School, said the nose has a large number of olfactory receptors, which implies our sense of smell could be even more powerful than the latest estimate.

Commenting on the research, he said: “The research goes a long way to addressing the capability of the human olfactory system, but there are still specific questions to be answered about exactly how many individual chemicals can be perceived.”

Fewer eggs during IVF treatment likely to cause miscarry (Health)

      The study analysed 124,351 IVF pregnancies between 1991 and 2008

The study analysed 124,351 IVF pregnancies between 1991 and 2008

Women who produce fewer eggs during IVF treatment are more likely to miscarry, research suggests.

Scientists analysed 124,351 IVF pregnancies between 1991 and 2008.

About 20% of pregnancies in women who produced fewer than four eggs after the ovarian stimulation phase of IVF ended in miscarriage.

The research indicated the quality of the eggs in these cases was poorer – clinicians said this information would help them to counsel patients.

IVF involves stimulating a patient’s ovarian cycle, extracting eggs from their ovaries, fertilising them with sperm in a laboratory, then transferring the embryo into the womb to develop.

Ovarian surgery risk

In the study, carried out at King’s College London and the University of Birmingham, the miscarriage rate fell to 15.5% for women who produced between four and nine eggs, and 13.8% for those with between 10 and 14 eggs.

The average risk of miscarriage across the population is 15%.

The co-author of the research, Dr Sesh Sunkara from the Reproduction Unit at King’s College London, said: “I think the information will empower women.

“IVF treatment can be a distressing experience, and miscarrying makes it even more agonising.”

Dr Sunkara said the study could indicate new risk factors such as ovarian surgery, which could increase miscarriage risk if it lowered the number of eggs a woman produced.

The fact women with fewer eggs had more miscarriages indicated the quality of the eggs must be lower, she said, as it was through such eggs miscarriages happened.

Prof Neil McClure, professor in obstetrics and gynaecology at Queen’s University, Belfast, said: “This study is vast in terms of its numbers, and reached a very logical conclusion.”

He said reduced egg production was linked to a woman’s age, as young women produced lots of healthy eggs, which decreased in number and quality with age.

Prof McClure said he thought the younger women in the study who produced fewer eggs did so because they were on the brink of an early menopause, which was “more common than we might think”.

Women who had miscarried after IVF and were worried about miscarrying again could opt for an egg donor, he said, adding that cutting down on smoking and eating a healthy diet would also help.

Help for clinicians

Prof Siobhan Quenby, professor of obstetrics at the University of Warwick, said: “It [the study] will be very helpful for me as I see a lot of people who have miscarried after IVF.”

She said uncovering the link between low numbers of eggs and egg quality was important to inform people in deciding whether to carry out another round of IVF, which costs on average about ?10,000 if done privately, or opt for an egg donor.

Prof Quenby added: “There is a lot of emotional trauma involved in miscarrying after IVF. It is really devastating for women who wait 10 years to have a baby and then with eight weeks to go they miscarry.

“You want to cry with them.”

Source BBC

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