Piles (haemorrhoids) are swellings that develop inside and around the back passage (anal canal). There is a network of small veins (blood vessels) within the lining of the anal canal. These veins sometimes become wider and engorged with more blood than usual. The engorged veins and the overlying tissue may then form into one or more swellings (piles). This might result in bleeding and discomfort if left untreated.