For two-legged creatures like us with our noses high above the ground, smell is no longer a vital sense in the same way as it is for our more distant relations among the mammals. For humankind, sight has taken first place. However, that does not prevent the sense of smell from being important to us in other ways.

“The sense of smell is unique, as it is so clearly connected to the brain’s emotional ­centre. Smells can facilitate learning and trigger memories”, says Ulf Ellervik, Professor of Bioorganic Chemistry.

In view of the power that smell has over our emotions, it is not surprising that we want to smell good. Our wish to gain the attention of those around us – like our ability to enjoy fragrances – has made perfumes and cosmetics the basis for a huge industry.

A scientific aura  

Perhaps to justify the price, products are sometimes underpinned by arguments that lend a scientific aura. One widely-circulated example is that perfume smells different from person to person, depending on the pH value of the skin.

“The pH value of the skin varies marginally between people. It hardly has an influence – if you have a markedly different pH value this is due to other circumstances”, says Ulf Ellervik.

However, there are other factors that may come into play, he points out, such as the body’s production of sebum. Smells bind to fat, so smells will bind for longer on people with oilier skin than on those who produce less sebum.

Certain perfume producers claim that their products interact with the body’s own scent signals, the so-called pheromones, and in this way create a totally unique fragrance.

“It is most likely to be a sham, or in any case very overestimated. There is, as yet, no hard evidence that we are affected by pheromones at all.”

While pheromones may not be a subject of everyday discussion in the perfume business, fragrance notes certainly are. A perfume is developed in three phases, it is said, depending on the evaporation rate of the ingredients involved: from the first transient top notes, via heart notes to the more long-lasting base notes. Among the first-mentioned are citrus and fruity fragrances whereas vanilla, musk and woody scents tend to remain on the skin for longer.

Is this true?

“It is true that chemicals evaporate at different rates. Smaller molecules are released faster than heavier ones and, if you are warm, they evaporate even faster.”

Meanwhile, Ulf Ellervik draws attention to another vantage point: to consider the perfumier’s mixing of chemicals as an art form, something like painting of cooking. Then there is no need to adopt a scientific approach.

“Regardless, it can be said that fragrance notes are an imprecise concept, even though there is something in it. Just like the perfume ­industry would like to pretend to be a little scientific. On the other hand, perfume manufacturers are skilled at producing combinations that many people like.”  

Perfumiers and chemists are also getting better at developing new synthetic fragrances in the lab, which opens the way for completely new smell experiences that can otherwise be difficult to extract, lily, for example. The possibility of producing animalistic fragrance notes, such as musk, provides ethical advantages. Chemists can also send in new, personally created fragrances to perfume companies.

“A colleague once managed to produce a chemical with a pleasant smell and he sent it in. Personally, I have only been able to produce disgusting scents, one was a really horrible mix of blue cheese and foot sweat…”

Can it be claimed that synthetically produced chemicals in perfumes are better or worse than the natural versions?

No, according to Ulf Ellervik, a certain synthetic molecule is exactly the same as one that comes from a natural source.

Alcohol, on the other hand, is another reason that perfumes have a somewhat sharp, pungent smell and that some are perceived as a little unnatural. It is needed, however, to dissolve scent substances and evaporates quite rapidly. Creams and oils can also act as scent bearers. Fats dissolve certain scent substances better and release them at a slower rate.

Hundreds of bacteria types on the skin

Whether we want to or not, we also smell of ourselves. Of sweat, for example. Bacteria flourish around armpits and genitals, as the sweat glands there produce substances that bacteria like.

They double in number every 20 minutes, explains Ulf Ellervik, and there can be several hundred strains. As a rule, these change slowly over time and differ between people. Thus, we stink in slightly different ways.

The bacteria found on feet flourish in the moist and enclosed environment of socks. These bacteria produce the classic foot sweat smell, whereas bacteria on the scalp can give off a weak scent of peach. On the rest of the body, the sweat glands only release water and different salts. There are also bacteria that protect us in different ways, but the smells are not so pronounced.

In the past, when ordinary people had neither soap nor running water, did we go around stinking the whole time?

“Well, the brain does not process information unnecessarily and quickly disconnects sensory experiences that don’t change. That’s one reason why you don’t smell your own perfume after a while.”

Natural can also smell good. Sun-warmed skin for example.

“This is because of the sun’s UV radiation, as when it hits the skin it creates special molecules that we perceive as the smell of sun-warmed skin. We experience a similar phenomenon after a rain shower on sun-warmed asphalt.”

Age and gender are factors

There are blinded studies which show that men and women smell a little differently, due to different concentrations of certain substances. Age is also a factor. At around the age of 40, the body begins to produce substances – which do not smell very pleasant – that younger people do not have as much of.

Most people can perceive 10 000 different smells without difficulty.

Fascinatingly, says Ulf Ellervik, smells do not actually exist – like colours they are a construct in the brain.

“The smell is only in your brain, and it is not certain that others perceive it in the same way as you. One amazing thing is that we can recognise the smell of molecules that have never existed – before they were synthesised in a laboratory.”