As the name of a perfume, ‘au naturel’ may not be the most original but it could be the best way to seduce a man, claim scientists.

Women should forget about buying expensive sexy scents and rely on their natural odour if they want a mate.

For the first time, researchers have found men’s testosterone levels actually increase in response to a woman’s natural smell when she is at her most fertile.

Previously women have been shown to be attracted to men’s body odour containing the natural pheromones or chemical signals that attract the opposite sex.

But now it seems the attraction is mutual, with evidence that women’s own body odour exudes signals that she is in a fertile stage of her natural cycle. 

A new study in the journal Psychological Science put the theory to the test based on mating behaviour found among animals.

Male testosterone levels are influenced by odour signals given off by female animals, particularly when they are at their most fertile, but the evidence has so far been lacking in humans.

Psychologists Saul Miller and Jon Maner, from Florida State University, carried out two studies in which women wore t-shirts for three nights during various phases of their menstrual cycles.

Altogether 68 male volunteers aged 18 to 23 years smelled one of the t-shirts that had been worn by a female participant.

In addition, some of the male volunteers were asked to smell clean t-shirts that had not been worn at all.

Saliva samples were taken from the men before and after they smelled the t-shirts to analyse testosterone levels.

Results revealed that men who smelled t-shirts of ovulating women – those at their most fertile stage – had the highest levels of testosterone.

Their levels were higher than men who smelled t-shirts worn by non-ovulating women or men who smelled the unworn garments.

The men in the study were also asked to rate the t-shirt odours on pleasantness.

They said the clothes worn by fertile women were the most pleasant smelling.

The authors said their research was the first to provide clear evidence that men actually react positively to women who are at their most fertile.

Dr Miller said: ‘In other words, it suggests that testosterone levels may be responsive to smells indicating when a woman is fertile.’

The psychologists conclude this biological response may promote mating-related behaviour by males.

Dr MIller added: ‘The relatively higher testosterone levels ariisng from exposure to ovulatory scents suggests that those scents might lead men to respond with greater mate-seeking behaviours that they would otherwise.

‘In addition, high testosterone levels are associated with competitiveness, dominance and risk-seeking, all traits typically valued by women – particularly women near their peak of reproductive fertility.’

It appears men rise to the challenge of the sexy signals given off by women at periods of peak fertility, increasing their testosterone levels in response and with assertive behaviour that is optimally attractive to women, says the report.

Previous research has found going on the Pill may blunt a woman’s sense of smell – and so her ability to pick an ideal mate.

This has led to suggestions that before committing to a man, a woman should come off the Pill, to allow her to work out whether her beau is as attractive as she believed.