Women's spending become more impulsive and less controlled as their monthly period approaches. Hormonal fluctuations, psychologists say, may lead to women spending more than they can afford, buying unwanted goods or feeling out of control with money.

Professor Karen Pine of the University of Hertfordshire is presenting the findings of her research Sheconomics: How women's emotions cost them money at the British Psychological Society Annual Conference today, 2 April 2009.

Professor Pine's survey asked more than 400 women about their spending in the previous seven days as well as information about their menstrual cycle. Women in the pre-menstrual phase of their cycle were more likely to score highly on questions regarding recent impulse spending, such as 'my spending has been out of control' or 'I have spent more than I could afford'. Some of the women reported high levels of over-spending at this time, e.g. in excess of £250.

The survey excluded women who were using hormonal contraception, such as pill-users, since this makes them less susceptible to variations resulting from the menstrual cycle.

"Hormonal fluctuations affect a range of cognitive and emotional responses in women" said Professor Pine. "It is well documented, for example, that women experience a rise in impulsive behaviour, anxiety and irritability during the pre-menstrual phase. This is the first study to show it that this affects their spending behaviour."

"Other studies of brain scans using fMRI have shown fluctuations in activity in the orbitofrontal cortex during the menstrual cycle" she said. "This is the part of the brain involved in emotional regulation that is also activated by monetary rewards. The effect of ovarian hormones on the brain may explain fluctuations in women's ability to keep their spending in check at certain times in their cycle."

The British Psychological Society Annual Conference is taking place at the Holiday Inn on Brighton seafront from 1- 3 April 2009.

British Psychological Society