Women are more prone to IBS than men
Having a period significantly worsens IBS symptoms and lowers women's pain thresholds, the study found.
Researchers suggest sex hormones may be to blame.
The study was carried out on 29 female IBS patients aged 21 to 44 by a team at the University Hospital of South Manchester.
A tiny balloon catheter was inserted into their rectums and inflated on each occasion to detect changes in rectal sensitivity.
They were also asked to keep a diary of their symptoms and their levels of anxiety and depression were measured.
The women reported more frequent bowel habits and lower general well-being during their period.
Their rectal sensitivity was also significantly increased, and women reported increased abdominal pain and bloating then, compared to other phases of the cycle.
However they did not show signs of being more depressed or anxious.
In an article in Gut magazine, the authors suggest the stomachs of women with IBS, which are acutely sensitive, may be further sensitised by other triggers such as hormones.
Increased sensitivity
Study co-ordinator Dr Lesley Houghton said: "IBS is a condition that primarily affects women as opposed to men.
"Studies show sex hormones may do different things to the gastrointestinal tract.
"We also know the symptoms of people with IBS vary over the menstrual cycle and tend to be worse around menses [period].
"It might be that people's guts become more sensitive at menses.
"It might be that sex hormones have a role to play and this might need to be addressed by the pharmaceuticals industry."
The team plans to carry out more research in this area to try to discover the role of sex hormones in intensifying the condition.
IBS involves not only pain, but also diarrhoea, or diarrhoea alternating with constipation.
Sufferers often desperately need to go to the toilet with little warning, which severely limits their lifestyle.
No-one knows what causes IBS, although it is suggested that stress can make it worse.
Most sufferers are advised to try to manage the condition by changing their diet and trying to reduce stress levels, as well as taking other medication.