Diarrhoea may occur as a symptom of your illness or it may also occur due to infection. Some medicines can cause diarrhoea. Sometimes severe constipation can be mistaken for diarrhoea: when the bowel is blocked by constipation, liquid faeces pass around the solid faeces (sometimes called overflow), so it may seem as though you have diarrhoea.
Diarrhoea caused by radiotherapy
Diarrhoea is a common temporary side effect of radiotherapy to the pelvis, and your doctor will prescribe medicine to help with it. If you have diarrhoea caused by radiotherapy, changing your diet is unlikely to help, and it’s important that you take the anti-diarrhoea medicines prescribed by your doctor.