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Male underarm sweat can reduce stress in women, as well as alter the timing and length of their menstrual cycles, concludes a new study in the June issue of Biology of Reproduction.
The role of pheromones
"Our study results tell us that there are pheromones produced in male underarms that have nothing to do with sex but can affect the physiology and mood of the recipient," says study co-authors George Preti, a member of the Monell Chemical Senses Centre and an adjunct professor at the University of Pennsylvania, USA.
Pheromones are chemical signals emitted by one animal that cause changes in behaviour or physiology in other animals, according to the study. The most well-known pheromones are those that influence sexual behaviour.
Study methodology
Preti and his colleague, Charles Wysocki, also from the Monell Chemical Sense Centre and the University of Pennsylvania, recruited 18 heterosexual women between the ages of 25 and 45 for the current study.
The women had regular menstrual cycles, normal hormone levels, regular sleep patterns, and had to be within 15 percent of their ideal body weight at the start of the study.
They were followed for three full menstrual cycles. During the first and third cycle, the researchers simply recorded the women's hormone levels using urine samples.
Male extract placed on upper lip
Within the first seven days of the second menstrual cycle, the women spent a day at the research centre. They either had a male extract or ethanol applied by a cotton pad to their upper lip area every two hours for a total of 12 hours. Half of the group received ethanol for the first six hours, and male extract for the remaining six hours. The other half was exposed to the substances in the reverse order.
The male extract was collected on cotton pads place under the arms of men who had voluntarily stopped using deodorant or any soap with fragrance for four weeks.
Ethanol was used as a control. In both cases, a similar scent was used to cover up the odour so the women didn't know what the substance was. Remarkably, none of the women figured out they were inhaling perspiration odours. Some believed they were involved in a study of alcohol, perfume, or even lemon floor wax.
Blood samples were taken every 10 minutes while they were at the research centre. The women were also asked to evaluate their moods while they were undergoing testing during the second cycle.
Reproductive hormone produced more readily
The researchers found that surges of luteinising hormone (LH), an important reproductive hormone, were produced in less time after exposure to the male underarm extract. Exposure to the male extract shortened the time between LH surges by 20 percent, according to the study. Changes in LH surges can change the length and timing of the menstrual cycle.
They also found that women exposed to the male extract reported feeling less tense and more relaxed.
"Much to our surprise, we also saw the mood changes," Preti says.
He says he and his colleagues hope to get further funding to isolate the exact chemicals in male perspiration that are responsible for these changes, which in the future might have some clinical applications in treating problems such as infertility.
Effect questioned
"The effect on the LH peak seems to be real. It was pretty consistent," says Dr Manvinder Singh, a reproductive endocrinologist at William Beaumont Hospital in Michigan, USA.
When it came to the mood changes, however, Singh wasn't as convinced.
"There could be an effect on mood, but the effect is slight," he says, adding, "We shouldn't market men's perspiration as a way to get women less tense.
