Haemorrhoids. Endoscope view of internal haemorrhoids in a patient's anus. Haemorrhoids are swollen veins in the lining of the anus. They are caused by increased pressure in these veins, usually due to the patient straining to expel hard faeces. They cause pain and bleeding on defecation. A diet high in fibre and fluids can help reduce their severity, and anti-inflammatory drugs can reduce the swelling. Severe cases of haemorrhoids require surgical treatment. This can include cryosurgery (freezing the veins off), sclerotherapy (blocking the veins with an irritant) and excision.