Women are more attractive to men when they are at their most fertile, according to a new survey.
A study involving hundreds of people found that a woman's attractiveness fluctuates depending on where she is in her menstrual cycle.
The hormonal shifts cause facial and vocal changes in women are at their most alluring near ovulation, when they are most fertile.
Women are most attractive when they are at their most fertile point in their menstrual cycle, according to the research
The research, published in the journal Hormones and Behavior, is the largest study to examine whether how attractive a woman seems changes over the course of her menstrual cycle.
More than 200 photographs were taken of women's faces at two separate points in their cycle in the study by three universities.
Their speaking voice was also recorded at both times and their hormone levels taken.
Five hundred men were asked to rate the pictures and voice samples and it was found women were at their most appealing when their progesterone was low and oestrogen levels were high.
Researchers said hormones may change blood flow, acne and puffiness that affect attractiveness
Assistant professor of anthropology at Pennsylvania State University David Puts, and the study's lead author, told the Huffington Post: 'The only time in the cycle when estradiol (oestrogen) levels are high and progesterone levels are simultaneously low is the late follicular phase, near ovulation when fertility is highest.'
A group of more than 500 women were also asked to rate the photographs based on flirtatiousness and attractiveness to men and the subjects scored higher when they were most fertile.
Professor Puts told the Huffington Post: '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.'
He said the difference could be caused by blood flow changes that affect facial colour, changes to acne or puffiness caused by water retention.
He added that it has been an advantage to our ancestors because women were able to
Nathan Pipitone, a psychologist at Adams State University in Colorado, told the website: 'This paper establishes conclusive evidence for how men and women rate other women as a function of their hormonal status.'
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