Citrus scent released during ovulation ‘makes women more attractive to men'
The discovery explains why women are often perceived as more attractive during this stage of the menstrual cycle, which is when fertility peaks.
Japanese scientists took sweat samples from 21 women at each of the four stages of the monthly cycle: menstrual, follicular, ovulatory and luteal. These were randomly presented to 21 men who assessed how the 84 different scents smelled to them and which ones they preferred.
A follow-up trial also asked the men to rate the attractiveness of women they were looking at on a screen while different body odour smells were wafting into their nose.
The findings revealed 98 chemicals that fluctuate in concentration throughout the menstrual cycle and identified three which are made more during ovulation.
E-geranylacetone, tetradecanoic acid and (Z)-9-hexadecenoic acid, the chemicals identified, are known to smell nice or play a role in the olfactory system of humans.
The first is a common ingredient in perfumes and smells woody, sweet and fruity, the second is waxy and soapy and is found in nutmeg and coconut oil, and the third is associated with body odour and is known to be musky.
The overall impact of these three chemicals is that women smelled less 'vinegary' and more 'fragrant' during ovulation, according to the men in the trial.
'We identified three body odour components that increased during women's ovulatory periods,' said Professor Kazushige Touhara from the University of Tokyo.
'When men sniffed a mix of those compounds and a model armpit odour, they reported those samples as less unpleasant, and accompanying images of women as more attractive and more feminine.'
Naturally-produced scents affecting behaviour
The men were also found to be less stressed, more comfortable and more relaxed when these chemicals were present at high levels.
'These results suggest that body odour may in some way contribute to communication between men and women,' Prof Touhara added.
Previous studies have found that women are considered more attractive to men while ovulating, and there have been suggestions that odour can play a role in this process. But this study is among the first to add scientific credence to the theory that the scents naturally produced by one person can alter the thought process and behaviour of another.
Pheromones have long been a staple of films and books as a way for an individual to win the affection of another but their existence among humans is an enduring scientific myth.
The Japanese scientists say this study does not 'conclusively say that the compounds are human pheromones' because it is not known yet if these are specific to people only which is needed to meet the definition of pheromones.
Pheremone-like compounds
Prof Touhara said: 'We were primarily focused on their behavioural or physiological impacts, in this case, the reduction of stress and change in impression when seeing faces.
'So, at this moment, we can say they may be pheromone-like compounds.'
The scientists write in their study, published in iScience, that it is possible this process may have evolved from the more crude pheromones of other species to create a 'communicative tool that positively affects emotions in males and induces relaxation and a positive impression toward females'.
'Such a role could function as a discreet but effective cross-sex olfactory signal in a highly developed human society governed by intellect rather than instinct,' they write.
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