Haemorrhoids, commonly known as piles, are swollen blood vessels in or around the anus and rectum. The haemorrhoidal veins are located in the lowest part of the rectum and the anus. Sometimes they swell so that the vein walls become stretched, thin, and irritated by passing bowel movements.
Haemorrhoids are classified into two general categories - internal and external.
1. Internal haemorrhoids
lie far enough inside the rectum that you can't see or feel them. They don't usually hurt because there are few pain-sensing nerves in the rectum. Bleeding may be the only sign that they are there. Internal haemorrhoids are deeper and initially form above a point 2-3 cm inside the back passage (anal canal) in the upper part of the anal canal.
2. External haemorrhoids
lie within the anus and are often uncomfortable. If an external haemorrhoid prolapses to the outside (usually in the course of passing a stool), you can see and feel it.
External haemorrhoids start off nearer the surface, below a point 2-3 cm inside the back passage.