Sunday 26 April 2015

Humans can recognise one trillion odours

Previously it was estimated that humans could smell 10,000 odours but now researchers say it is more like one trillion

Cockburn's wine taster and blender Manuel Rocha is known for his incredible sense of smell, but scientists believe everyone is better than they think

Humans have a far greater sense of smell than previously thought but daily showers and fridges, which mask bad odours, have stopped us noticing, scientists believe.

Previously it was estimated that we could smell 10,000 odours but now researchers say it is more like one trillion.

Scientists believe our sense of smell is much closer to that of animals than appreciated, but we no longer pay attention because smells are often hidden, meaning that important information is lost.

“Humans have not lost their sense of smell. We are just not aware of how good we are at smelling and are just not using this sense to our full potential,” said Dr Leslie Vosshall, one of the report authors at Rockefeller University in New York.

“Our paper shows that humans have a dramatically better sense of smell than previously assumed.

“It’s there for us to use. Everyone should go outside and smell things and be more engaged with smells.”

The sense of smell evolved over millions of years and our human ancestors would have used it as a tool to spot disease, avoid rotten meat and poisonous plants and sniff out food.

However our upright posture lifted our noses far from the ground where most smells originate, diluting scent molecules in the air.

And today many smells which still give us hints about rot and poor hygiene are masked behind perfumes, air fresheners and deodorants.

Researchers said this could explain why people believe that smell is unimportant, compared to hearing and vision.

Yet smells are still having a greater impact than we realise, warning of danger, triggering memories and even helping us choose a partner.

Many studies have shown that pheromones emitted from the sweat glands play an important role in physical attraction.

Dr Craig Roberts, a senior lecturer in psychology at the University of Stirling, believes that certain medications, such as the pill, can suppress our natural ability to pick these signals.

“We all use smell more than we realise, sometimes in ways we don’t think much about, such as when choosing partners.

“Of course we don’t realise we’re doing exactly this, but some people smell nicer than others and the research shows our preference might result in choice of compatible mates.

“Our olfactory sense is clearly more sensitive and more complex than we previously believed.”

To discover how well humans can smell, scientists enlisted a group of 26 volunteers and tested their ability to distinguish between complex mixtures of scents.

They used 128 different odorant molecules including smells which evoke grass, citrus, orange, anise and spearmint.

Participants were presented with mixtures of up to 30 odour molecules in three vials.

Two were the same, one had slightly different molecules. They were asked to pick which the odd one out.

The results, published in the journal Science, show that on average participants could tell the difference between mixtures when half of the molecules were different.

From there, they extrapolated 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 their 128 odorants and found it was close to one trillion.

Dr Andreas Keller, who led the research at Rockefeller's Laboratory of Neurogenetics, said: "The message here is that we have more sensitivity in our sense of smell than for which we give ourselves credit.

"We just don't pay attention to it and don't use it in everyday life."

Dr Vosshall said she doubts individuals are exposed to a trillion smells on a daily basis.

"But I like to think that it's incredibly useful to have that capacity, because the world is always changing," she says.

“Plants are evolving new smells. Perfume companies are making new scents. You might move to some part of the world where you've never encountered the fruits and vegetables and flowers that grow there. But your nose is ready.”

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