When Marilyn Monroe sang Happy Birthday, Mr. President to President John F. Kennedy in 1962, surely her voice sent his skin tingling. The sound of a woman’s voice as she sings has that power — it’s sensuous, sultry, powerful, and soft. But a woman doesn’t need to be singing to have that effect on men, according to a new study. All they have to do is speak to a guy at the right time of the month.

The hormonal changes that accompany a woman’s menstrual cycle also alter the sound of her voice, just enough so that both men and women are unconsciously able to pick up on the differences, which signal when she’s most fertile, thus sending an abundance of electrical activity through the men and women’s skin and increasing their heart rate, too. In other words, a woman at the peak of her fertility can make a man’s skin (and woman’s) tingle just by talking to him or her.

The study shows that our own physiology has these longstanding, built-in mechanisms that assist in reproduction — even if our society isn’t in that mode anymore. Not only were there more electrical currents running through men and women’s skin, but they also found the fertile women’s voices more attractive.

“A man’s ability to identify and respond to a fertile woman confers him a potential reproductive advantage when choosing between potential mates,” study author Dr. Melanie Shoup-Knox, of James Madison University in Virginia, told The Telegraph. “Women, on the other hand, may get a competitive advantage from detecting the fertility status of other females.”

Shoup-Knox and her colleague Dr. R. Nathan Pipitone enlisted a group of men and women, as well as some gay men, to listen to recordings of women’s voices from different times of their menstrual cycle — some of the women were taking hormonal contraception as well. They found that when a woman was at the peak of her fertility, the electrical activity in participants’ skin increased by about 20 percent while their heart rates sped up by about five percent. These effects occurred as soon as five seconds of hearing the woman’s voice, long before the person consciously knew what was happening.

The findings are the latest in a body of research seeking to understand the underlying physiological processes that lead to attraction and reproduction. Other studies have found that with being highly fertile comes a higher pitched voice and a more attractive smell. And one study from 2012 also found that men rated women’s faces as more attractive when they were most fertile. Many of the researchers from these studies suggest that if someone is able to pick up on these cues, they’ll have more reproductive success. But really, even if they could, it’s only one piece of the mating puzzle.

Source: Shoup-Knox M, Pipitone R. Physiological changes in response to hearing female voices recorded at high fertility. Physiology & Behavior. 2014.