Taking birth control pills alters men’s attractiveness to women, mimicking the hormonal effects of pregnancy in making women more attracted to healthy faces.

UK researchers at the Universities of St. Andrews and Aberdeen say that the finding reflects an internal mechanism to avoid maternal illness.

Previous studies by psychologists at the University of St. Andrews’ Perception Lab found that women at their most fertile times tend to choose masculine-looking men, presumably to secure strong genes.

The new study shows that women with high levels of the hormone progesterone but low levels of fertility—such as pregnant women, those taking oral contraceptives and those in their third or fourth week of their monthly menstrual cycle—are choosy in different ways: they prefer both healthy-looking men and women.

“Pregnant women and women with raised progesterone levels were more attracted to the men who appeared healthier,” says study first author Ben Jones. “Our findings suggest that pregnancy—or when a woman is in a similar hormonal state—trigger strategies within the body for avoiding illness during social interactions.”

More here.