Recent study has shown that lap dancers at the peak of their fertility earn more in tips compared to their colleagues who are either on the Pill or in the non-fertile periods of their menstrual cycle.

Comparing the earnings of lap dancers who were menstruating naturally with others taking the contraceptive pill, researchers at the University Of New Mexico said they suspect that pheromones, the subtle scent signals that in animals play a key role in sexual attractiveness, night be involved.

"During the non-fertile periods of their menstrual cycle, dancers not on the Pill earned much the same as those using the contraceptive," said Dr. Geoffrey Miller of their findings.

However, Miller added, when the naturally cycling dancers entered their fertile period, their tips became significantly more generous.

According to Miller, their findings was the first to show that oestrus has a "real effect on women's earnings," adding that previous research has shown that women's faces, scent and clothing become more attractive in oestrus.

Previously, studies indicate that women dress and behave differently when they are most fertile.