New research is suggesting a there is possibly a link between allergic conditions such as asthma and hay fever and irregular periods.
In a survey of more than 8,500 wome, aged 25-42, a Norwegian team has found that rates of asthma and allergy were far higher in women who had irregular rather than regular periods.
The Thorax study points to metabolic problems, such as insulin resistance, as an underlying cause for both.
The team say their findings add further evidence to the argument that female hormones might play a role in allergic diseases.
The possibility that the trend might have been down to the allergy medication the women were using was discounted as the irregularity was also seen among women whose symptoms were not being treated.
Dr Cecilie Svanes and colleagues from the Haukeland Hospital in Bergen, Norway, in their study questioned the women about their respiratory health and menstrual cycles between 1999 and 2001.
About one in four women (23%) had irregular periods - 14% among those aged 25 to 42 and 37% among those aged between 43 and 54, and among the younger women, irregular periods were most common in those who weighed the most or were the shortest or tallest.
Among the older women, they were associated with smoking and the timing of the menopause.
The researchers found after taking into account a number of factors, that the rates of asthma and allergy were significantly higher in younger women with irregular periods than in those with regular periods.
They said irregular periods were often caused by polycystic ovary syndrome (PCOS) - a condition where the ovaries have abnormal cysts.
PCOS has been linked to a disturbance of the normal metabolism that can be treated with drugs such as metformin to aid the processing of sugars in the body.