Scientists reported on Wednesday a remarkable new side effect of the Pill - it changes women’s preference in men.

Psychologists at the University of St. Andrews in Scotland asked 1570 young women on oral contraceptives and 1325 women who were not, to choose between healthy and less healthy male faces. The same face was presented twice, one image glowing with apparent health, the other looking pale and unwell.

All women preferred the healthier face on average but those on the Pill were significantly more choosy. “Women using oral contraceptives expressed stronger attraction to apparent health than women not using oral contraceptives,” the researchers reported in the Proceedings of the Royal Society.

The team, led by Ben Jones and David Perrett, also found in other studies that women’s preference for apparently healthy faces was stronger during the post-ovulation phase of the menstrual cycle and during pregnancy.

“Collectively, these findings suggest that increased attraction to apparent health in faces coincides with conditions that are characterised by raised progesterone levels, rather than conditions that are characterised by high fertility,” they said.

Women, they suggested, may have evolved strategies - triggered by raised progesterone levels - to reduce the risk of infection disrupting development of the unborn baby when their immune system is weaker than normal.