The science of SMELL: Expert reveals truth behind smelly feet and armpits

Some people have a force-field of terrible breath or feet that smell so repellent that insoles are never enough to dampen the disgusting odour.

And while people have their own unique scent, it is a surprisingly select cocktail of chemicals that create the distinctive and disgusting aromas associated with bad body odour.

Now, a secondary school teacher has created an infographic to pinpoint the compounds and the particular smells they bring to underarm odours and even flatulence.

The anonymous blogger started publishing his infographics four months ago after creating some posters to brighten up his classroom and hopes to explain the chemistry of everyday substances and problems on his Compound Interest blog, where he also sells his creations.

It is well known that in most cases, halitosis, or bad breath, is the product of bacteria in the mouth, which produce waste products and chemical compounds.

But many people don’t know that the main offenders are volatile sulphur compounds, including hydrogen sulphide, which smells of rotten eggs, methanethiol, which resembles gone-off cabbage and dimethyl sulphide, which is a little bit like garlic.

At low levels, these compounds aren’t detected by the human nose, but it doesn’t take a great deal for them to become noticeable and put off a partner.

Certain foods and drinks can also make the problem worse – or at least more distinctive. As well as the three primary offenders, the compound called 3-mercapto-3-methylbutylformate is produced when someone drinks coffee and gives their breath a nasty tang.

Garlic breath is attributed to allyl methyl sulphide – a product of the breakdown of garlic – and eating meat and fish can make your breath smell like a rotting corpse.

 

This is because the bacteria that produce volatile sulphur compounds thrive on proteins and produce extra compounds such as cadaverine and putrescine, which smell of rotting human bodies and fish.

In a rather disgusting study, it was ‘proved’ that sulphur-containing organic compounds are produced in the digestive system and are to blame for flatulence.

Hydrogen sulphide, methanethiol and dimethyl sulphide – all of which contribute to bad breath – are again the main offenders.

Experts used a combination of gas chromatography and ‘smell experts’ to identify the compounds.

 

 

There are approximately one million bacteria per square centimetre on your underarms, which can smell if left unwashed.

 

 

There are two organic compounds responsible for undesirable odours that don’t contain sulphur. One is 3-methyl-2-hexenoic acid – which is recognisable as that nasty sweaty smell and has been described by experts as ‘goat-like’ – and 3-hydroxy-3-methylhexanoic acid that makes a cumin-like smell.

Another compound called 3-methyl-3-sulfanylhexan-1-ol along with other sulphurous compounds provides an onion-like note.

Like with underarms, the presence of sweat provides a helpful environment for bacteria to thrive and produce noxious compounds.

Two of the main contributors to ‘cheesy’ feet are propanoic acid and isovaleric acid.

Propanoic acid is described as ‘pungent, sour and rancid’, while the cheesy smell comes from isovaleric acid, which is also said to smell ‘rancid and fermented’. Isovaleric acid is produced as the result of bacteria also found in certain pungent cheeses.