Not to be sniffed at: The human nose can distinguish between over one trillion odours - a billion times more than we'd thought


Science Editor

A typical person can smell at least one trillion different odours – a billion-fold greater than previously thought – according to the first scientific study to accurately estimate the olfactory power of the human nose.

The remarkable and unforeseen ability of the nose to distinguish between different kinds of odour has been revealed in a pioneering study showing that humans are not to be sniffed at when it comes to the sense of smell.

It has been widely accepted for nearly a century that humans are able to discriminate between no more than about 10,000 odours, but the latest findings show that the true number is much greater, conservatively estimated at one trillion, or 1,000,000,000,000.

This would make the human sense of smell more discriminatory than human colour vision, which can distinguish between 2.3 million and 7.5 million colour variations, or human hearing, which can discriminate between about 340,000 sound tones.

“We have debunked an old idea that humans can only smell about 10,000 odours and we’re the first to come up with an accurate number, which is far, far higher than anyone had calculated,” said Professor Leslie Vosshall of the Rockefeller University in New York.

“The nose is really like a massive broadband technology that can take in huge amounts of information and pass it on to the brain. It is the only part of us that connects directly to the brain,” Professor Vosshall said.

“Our analysis shows that the human capacity for discriminating smells is much larger than anyone anticipated. Everyone in the field had the general sense that this number was ludicrously small, but [we were] the first to put the number to a real scientific test,” she said.

The 10,000 figure came from a 1927 study which had not been seriously challenged until now. “Objectively, everybody should have known that the 10,000 number had to be wrong,” Professor Vosshall added.

The latest study, published in the journal Science, involved the creation of unique combinations of smells derived from mixtures of 128 odour molecules derived from scents such as orange, anise and spearmint.

Volunteers were asked if distinguish between different combinations of these odour mixtures, which were made from groups of 10, 20 or 30 different odour molecules.

The volunteers were given three vials to smell, two of which were identical, and were asked to pick the odd one out. The third vial started out the same as the other two but was gradually altered to become more different. This enabled the scientists to gradually manipulate the molecular composition of each odour to eventually make it different enough for the nose to make a clear distinction.

Each of the 26 volunteers – 17 women and nine men – had to make 264 comparisons and, from these combined results, the scientists were able to make an extrapolation that gave them a conservative estimate of the overall olfactory power of the human nose.

“Our trick is we use mixtures of odour molecules, and we use the percentage of overlap between two mixtures to measure the sensitivity of a person’s sense of smell,” said co-author Andreas Keller of Rockefeller’s laboratory of neurogenetics and behaviour.

“We didn’t want them to be explicitly recognisable, so most of our mixtures were pretty nasty and weird. We wanted people to pay attention to ‘here’s this really complex thing – can I pick another complex thing as being different?’,” Dr Keller said.

“The message here is that we have more sensitivity in our sense of smell than we give ourselves credit. We just don’t pay attention to it and don’t use it in everyday life,” he said.

Human smell relies on two small odour-detecting patches in the upper nasal chamber each containing about five or six million receptor cells – comprising of 400 receptor types – which send signals directly to the brain via the olfactory bulb, attached to the base of the brain. 

By comparison, the rabbit has 100 million olfactory receptor cells and the dog has some 220 million. This helps to explain why humans are much poorer at smelling than other animals, Professor Vosshall said.

“We show that humans have a good sense of smell that’s not been appreciated before but other animals are still better – rats are better than humans, but humans are still pretty good,” she said.

“I like to think that it’s incredibly useful to have that capacity, because the world is always changing. Plants are evolving new smells. Perfume companies are making new scents.”

The sun rises over St Andrews golf course, but will it be a new dawn for the Royal and Ancient Golf Club?
sportAnd it's Yes to women (at the R&A)
Arts and Entertainment
Friends is celebrating its 20th anniversary this year
tvSeries celebrates 20th anniversary
Yaya Touré (left) and Bayern Munich’s Spanish defender Juan Bernat
footballToure's lack of defensive work is big problem for City
voicesApple continually kill off smaller app developers, and that's no good for anyone
Arts and Entertainment
Liam Neeson said he wouldn't

Liam Neeson's Downton dreams

Wembley Stadium
footballNews follows deal with Germany
Arts and Entertainment
A spell in the sun: Emma Stone and Colin Firth star in ‘Magic in the Moonlight’
filmReview: Magic In The Moonlight
ebooksAn unforgettable anthology of contemporary reportage
A 'Sir Alex Feguson' tattoo

Arts and Entertainment
Ben Whishaw is replacing Colin Firth as the voice of Paddington Bear

Thriller is set in the secret world of British espionage

Life and Style

ScienceGallery: Otherwise known as 'the best damn photos of space you'll see till 2015'
Life and Style

Bomber jacket worn by Mary Berry sells out within an hour

Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Volunteer your expertise as Trustee for The Society of Experimental Biology

Unpaid Voluntary Position : Reach Volunteering: Promising volunteer Trustee op...

Email Designer

£30000 - £35000 Per Annum: Clearwater People Solutions Ltd: Our client is curr...

Psychology Teacher

£110 - £130 per hour: Randstad Education Reading: Psychology Teacher needed fo...

Food Technology Teacher

£85 - £120 per day: Randstad Education Cheshire: Randstad Education are curren...

Day In a Page

Mystery of the Ground Zero wedding photo

A shot in the dark

Mystery of the wedding photo from Ground Zero
His life, the universe and everything

His life, the universe and everything

New biography sheds light on comic genius of Douglas Adams
Save us from small screen superheroes

Save us from small screen superheroes

Shows like Agents of S.H.I.E.L.D are little more than marketing tools
Reach for the skies

Reach for the skies

From pools to football pitches, rooftop living is looking up
These are the 12 best hotel spas in the UK

12 best hotel spas in the UK

Some hotels go all out on facilities; others stand out for the sheer quality of treatments
These Iranian-controlled Shia militias used to specialise in killing American soldiers. Now they are fighting Isis, backed up by US airstrikes

Widespread fear of Isis is producing strange bedfellows

Iranian-controlled Shia militias that used to kill American soldiers are now fighting Isis, helped by US airstrikes
Topshop goes part Athena poster, part last spring Prada

Topshop goes part Athena poster, part last spring Prada

Shoppers don't come to Topshop for the unique
How to make a Lego masterpiece

How to make a Lego masterpiece

Toy breaks out of the nursery and heads for the gallery
Meet the ‘Endies’ – city dwellers who are too poor to have fun

Meet the ‘Endies’ – city dwellers who are too poor to have fun

Urbanites are cursed with an acronym pointing to Employed but No Disposable Income or Savings
Paisley’s decision to make peace with IRA enemies might remind the Arabs of Sadat

Ian Paisley’s decision to make peace with his IRA enemies

His Save Ulster from Sodomy campaign would surely have been supported by many a Sunni imam
'She was a singer, a superstar, an addict, but to me, her mother, she is simply Amy'

'She was a singer, a superstar, an addict, but to me, her mother, she is simply Amy'

Exclusive extract from Janis Winehouse's poignant new memoir
Is this the role to win Cumberbatch an Oscar?

Is this the role to win Cumberbatch an Oscar?

The Imitation Game, film review
England and Roy Hodgson take a joint step towards redemption in Basel

England and Hodgson take a joint step towards redemption

Welbeck double puts England on the road to Euro 2016
Relatives fight over Vivian Maier’s rare photos

Relatives fight over Vivian Maier’s rare photos

Pictures removed from public view as courts decide ownership
‘Fashion has to be fun. It’s a big business, not a cure for cancer’

‘Fashion has to be fun. It’s a big business, not a cure for cancer’

Donatella Versace at New York Fashion Week