Is the perfume industry looking for fragrances in the wrong place? The most seductive scents might come from ourselves, finds Mairi Macleod

IN ELIZABETHAN England, it was common practice for a maiden to peel an apple, place a slice in her armpit to absorb the smell and then present it to a potential suitor as a memento. Traditional Balkan dancing follows a similar principle. In an activity akin to Morris dancing, but with added odour, men put handkerchiefs in their armpits, work up a sweat by dancing hard and then wave their hankies under the noses of young females.

Throughout history and across cultures, body odour has played a key role in attraction, just as it does with many other animals. Yet modern societies tend not to appreciate nature’s perfume. Many of us go to considerable lengths to expunge our personal smells and replace them with ones we consider to be more appealing. Instead of apples in our armpits, we have deodorants and perfumes that are marketed as smelling of innocence, vivacity, sophistication or whatever attributes we believe will make us more alluring.

Is the multibillion-dollar fragrance industry missing a trick? As we discover which elements of body odour are attractive and to whom, the commercial potential of these chemicals is becoming increasingly apparent. Most people don’t want to smell of sweat, but it can only be a matter of time before some components of our natural perfumes are bottled.

You might think of yourself as a primarily visual animal, relying little on your sense of smell, but in recent years the idea that olfactory communication is not important in humans has been challenged. In fact, we possess more apocrine sweat glands than other apes. These are concentrated in the armpits along with springy hair to promote bacterial growth, which helps create body odour, and that has led to humans being labelled the “scented ape”.

Our sense of smell is also more sensitive and discerning than it was thought to be, especially when it comes to sniffing out information about other people. Women’s noses tend to be more sensitive than men’s, but each sex is particularly adept at decoding the messages contained in the odours of the other. Blind tests reveal that a person’s smell gives an indication of their sex, age, diet and some aspects of their health. It has even been claimed that we can smell fear and anxiety (New Scientist, 17 September 2011, p 44).

More relevant for perfumers is the recent discovery that our natural smells communicate information about our personalities. Agnieszka Sorokowska at the University of Wroclaw in Poland and her colleagues got 60 men and women to complete personality tests and then to wear T-shirts in bed for three nights. During this time, they were asked to sleep alone and to avoid smoking, using scented products or consuming smelly foods and alcohol. A different group of 200 men and women then sniffed the T-shirts and rated their wearers on various character traits. Their assessments were most astute when it came to judging levels of neuroticism, extroversion and dominance (European Journal of Personality, DOI: 10.1002/per.848). “Neuroticism and extroversion are very emotional traits and might change sweating rates and the composition of bacteria in the armpits, thus changing how a person smells,” says Sorokowska. Dominance, she adds, is associated with higher levels of some hormones with metabolites that could influence body odour.

People seem to have preferences when it comes to these scents. Women tend to prefer the smell of dominant men and are particularly attracted to the smell of dominance during the most fertile stage of their menstrual cycle, according to research by Craig Roberts of the University of Stirling, UK, and Jan Havlícek of Charles University in Prague, Czech Republic (Biology Letters, vol 1, p 256). This could be a useful predilection, says Roberts, because a dominant man may provide more resources for his partner and offspring. Dominance might also be linked with higher levels of testosterone, which is thought to indicate genetic quality, say the researchers.

Women also tend to prefer the smell of men who have more symmetrical bodies (Evolution and Human Behavior, vol 20, p 175). High body and facial symmetry is thought to indicate an ability to withstand environmental stresses, such as infection or toxins, also a sign of genetic quality.

Men, in turn, have preferences when it comes to women’s odours. Havlícek and his colleagues found that women tend to smell least appealing to men during menstruation and most attractive when they are ovulating (Ethology, vol 112, p 81). “The changes in smell are quite subtle and the variance [in odour attractiveness] between individual women is much greater than within individuals,” says Havlícek. Nevertheless, it seems that men can smell women’s fertility to some extent, at least subconsciously, and they like it.

Roberts sees potential for perfume manufacturers to cash in here. For instance, the compounds responsible for making women smell more attractive during their fertile phase could be included in fragrances. Likewise, the chemicals that make symmetrical men smell good could become ingredients in aftershave.

These compounds indicating fertility and symmetry haven’t yet been identified, but we may be close to pinning down the essence of dominance. In mice, dominant males produce high levels of androstenes, which are breakdown products of androgen steroids, the group of hormones to which testosterone belongs. Several studies suggest that these compounds can be attractive to women. In a speed-dating experiment, for example, Roberts and Tamsin Saxton of the University of Abertay Dundee, UK, found that women who had androstene dabbed on their top lip rated a given man more highly than those who received a water control or clove oil, which blocks out the smell of androstenes (Hormones and Behavior, vol 54, p 597).

In Patrick Süskind’s 1985 novel Perfume, the main character goes to extreme and murderous lengths to create the ultimate fragrance, one that captures the sublime beauty of the human soul such that its wearer will be loved by all. Unfortunately, in real life that fantasy falls at the first hurdle. It turns out that the scent of androstenes is not universally appealing. Not all women fall for the androstene trick: some actually find these chemicals unpleasant and a minority cannot smell them at all. Preferences for some other aspects of body odour are even more idiosyncratic.

Differences in taste are particularly strong when it comes to the major histocompatibility complex (MHC), molecules involved in immune system functioning. People prefer the smell of those of the opposite sex whose MHC genes are different from their own (New Scientist, 10 February 2001, p 36). “In our evolutionary past, humans would have lived in small groups where the risk of inbreeding was high, so a method of distinguishing the most dissimilar mates would have been useful,” says Claus Wedekind at the University of Lausanne, Switzerland, who made the discovery (Proceedings of the Royal Society B, vol 260, p 245). Another possibility, he says, is that children of parents with differing MHC will have immune systems capable of fighting a wider range of pathogens.

The exact mechanism through which MHC affects our body odour remains unclear. Wedekind thinks it could be down to the influence of the skin’s MHC on the bacterial community that can thrive there, which in turn affects the smelly substances that are produced. Another possibility is that the smells come from peptide ligands, the business end of the protein molecules involved in the MHC-mediated immune response. It is a sign of the commercial potential of this work that there are already two patents covering the use of these peptides in the customisation of scent (WO/2003/090705 and WO/2001/081374).

But even if we can pinpoint the chemicals associated with our MHC-based odours, the perfect bespoke perfume is unlikely to rely on them alone, says August Hämmerli of the Swiss Federal Institute of Technology in Zurich. “An MHC-based perfume will not necessarily make the wearer more attractive,” he says.

It might increase your chances of finding a compatible mate, but at the price of making you smell unappealing to others. Wedekind suspects that this may be exactly what we are trying to avoid when we wash and use perfumes. “In one of our experiments, we presented the same six [body] odours to 100 people and each of the odours was excellent to some and very bad to others, so maybe we just don’t want to risk smelling bad to some,” he says.

But there is another way in which MHC might help perfumers to tailor their products. MHC genotype affects preferences for odours other than body smells. In 2001, when Wedekind was still at the University of Bern in Switzerland, he and his colleague Manfred Milinski published results from a study in which they asked 137 men and women for their views on 36 perfume ingredients. They found that people’s preferences for scents they would choose for themselves were linked with their MHC genotypes (Behavioral Ecology, vol 12, p 140).

Last year, Hämmerli and his colleagues extended this research. Using the same set of perfume ingredients and genetic markers, they found that MHC-based preferences were stronger when presented in the context of sexual communication than they were in a neutral context. They suggested that instead of simply targeting perfumes crudely to groups based on factors such as sex, age and income, manufacturers could customise and sell scents according to MHC preferences (International Journal of Cosmetic Science, vol 34, p 161). “Our work is offering an applied starting point of how an MHC-based perfume could actually be created,” says Hämmerli.

Although MHC influences the perfumes we prefer for ourselves, Wedekind and Milinski found that it had no bearing on the scents people chose for their partner. This suggests that MHC does not directly affect how particular chemicals smell. Instead, it seems, participants in the experiment were subconsciously choosing scents that complemented their natural body odour rather than masking it. “The message is clear,” says Havlícek. “Don’t buy perfume for your lover, let them choose it themselves.”

More evidence that we do this comes from research by a group including Havlícek, his Charles University colleague Pavlina Lenochova and Roberts. They asked people to rate the smell of others first without and then with a perfume they supplied. “We found that people smell more pleasant and attractive when they use perfume, but it improved the smell of some more than others. Some actually smelled worse wearing perfume,” says Havlícek.

This was clearly due to interactions between the perfume and the wearer’s own smell, because the perfumes that smellers ranked most pleasant from the bottle were not necessarily the ones they liked best when people wore them. What’s more, subjects were rated as smelling better when wearing their own perfume than an assigned one, even when the latter had previously been judged as being more pleasant, again suggesting that people are able to choose scents to complement their own body odour (PLoS One, vol 7, p e33810).

This may make things more difficult for perfume manufacturers trying to cash in on any insights into body odour and smell preferences. “It’s not as simple as identifying and including particular compounds in perfume,” says Havlícek. “My guess is that there are mixtures of compounds interacting with each other, and that concentrations and ratios are also important.”

Perfumers are already aware that the attractiveness of a scent cannot be assessed simply by sniffing the bottle. “Many factors affect the behaviour [of perfume] on human skin,” says Matthijs van de Waal, who is based in Geneva, Switzerland, and has been creating scents for 45 years. “The most relevant, according to my observations, is diet.” Besides, he says, although international perfume houses like to take a global approach with their leading brands, they recognise that there are cultural differences and they already produce fragrances that are targeted to meet different regional preferences.

Customisation and niche marketing looks like the future as perfumers incorporate these findings into fragrance production. It is surely only a matter of time until personalised perfumes become as familiar as personalised medicine.

A person’s natural scent can signal their dominance and fertility

Traits like extroversion may affect your body odour

The inclination to hide our natural body odours is very strong. One study found that 79 per cent of women and 60 per cent of men reported using a deodorant every day, while 44 per cent of women also used perfume on a daily basis (Review of General Psychology, vol 14, p 318). These artificial scents can have a profound influence on our behaviour and the way others see us.

In one study, a team led by Takahiro Higuchi of the Tokyo Metropolitan University in Japan, filmed a woman interviewing a series of other women, half of whom applied perfume in the middle of the interview. The performances were then rated by another group of women. Although unaware of the perfume application, they noticed that the interviewees who had used scent were less likely to shift in their seats, fiddle with their hair and display other signs of nervousness. Overall, they rated them as more confident (International Journal of Psychology, vol 40, p 90).

In another experiment, Craig Roberts at the University of Stirling, UK, and colleagues allocated 35 men either a fully formulated deodorant or an odourless placebo and told them to avoid other fragrances. ” There was no difference between the groups of men in how attractive they were, as rated by an independent panel of women judges from photos,” says Roberts.

After three days, however, the confidence of the men using the placebo plummeted and they considered themselves to be less attractive. Women also thought them less attractive on the basis of only a video of the men talking about their holidays (International Journal of Cosmetic Science, vol 31, p 47).

By Mairi Macleod

Mairi Macleod is a freelance journalist based in Edinburgh, UK