Men find women more attractive near ovulation, when they`re most fertile, a new study has found suggesting that hormonal shifts may cause facial and vocal changes in females.

In the largest study yet to look at whether a woman`s allure changes over the course of her menstrual cycle, scientists noted that ratings of attractiveness were related to hormonal shifts, which bring about various physiological and behavioural changes.

Researchers took photographs of 202 women`s faces and made recordings of their speaking voices at two points in their menstrual cycles.

They also took saliva samples to measure hormone levels during both sampling sessions. More than 500 men rated the attractiveness of the women`s faces and voices from one of the two sessions.

The ratings from the first session were averaged for each woman and then compared with ratings for her second session.

Men rated faces and voices as more attractive when women`s progesterone levels were low and estradiol (estrogen) levels were high.

"The only time in the cycle when estradiol levels are high and progesterone levels are simultaneously low is the late follicular phase, near ovulation when fertility is highest," said the study`s lead author David Puts, an assistant professor of anthropology at Pennsylvania State University.

A group of more than 500 women were also asked to rate women`s attractiveness across their cycles.

They scored the photographs and vocal recordings based on two measures: flirtatiousness and attractiveness to men. Women rated the subjects higher on both measures when the subjects were in their more fertile phase.

"We learned beyond a reasonable doubt that women`s faces and voices change over the menstrual cycle, and that both men and women perceive this as changes in attractiveness," Puts told the website.

"This paper establishes conclusive evidence for how men and women rate other women as a function of their hormonal status," Nathan Pipitone, a psychologist at Adams State University in Colorado who studies human mating and voice attractiveness, agreed.

Pipitone, who was not involved in the research, said the study`s large sample size and measure of hormone levels strengthen its conclusions.
Research has suggested hormones, indeed, alter facial and vocal features.

The larynx, or voice box, has estrogen and progesterone receptors, and puberty, pregnancy, menopause, hormone replacement therapy and hormonal contraceptive use have all been shown to change women`s voices, the study authors said.

The new research was published in the journal Hormones and Behavior.