Haemorrhoids. Artwork of a transverse section of the anus showing internal and external haemorrhoids. These are swollen veins (red) in the lining of the anus; they may occur close to the anal opening (bottom centre), in which case they are called external or protruding, or higher in the anal canal (internal). They are common in pregnancy due to the pressure of the foetus on the veins in the anus. Some people have a congenital weakness of the veins in this area which may contribute to the development of haemorrhoids. Mild cases are controlled by drinking plenty of fluids and a high-fibre diet. Protruding haemorrhoids are usually removed surgically.