Haemorrhoids 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.

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. Sometimes internal haemorrhoids prolapse, or enlarge and protrude outside the anal sphincter. If so, you may be able to see or feel them as moist, pink pads of skin that are pinker than the surrounding area. Prolapsed haemorrhoids may hurt because they become irritated by rubbing from clothing and sitting. They usually recede into the rectum on their own; if they don’t, they can be gently pushed back into place.

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. Blood clots sometimes form within prolapsed external haemorrhoids, causing an extremely painful condition called a thrombosis. If an external haemorrhoid becomes thrombosed, it can look rather frightening, turning purple or blue, and could possibly bleed. Despite their appearance, thrombosed haemorrhoids are usually not serious and will resolve themselves in about a week. If the pain is unbearable, the thrombosed haemorrhoid can be removed with surgery, which stops the pain.

Anal bleeding and pain of any sort is alarming and should be evaluated; it can indicate a life-threatening condition, such as colorectal cancer. Haemorrhoids are the main cause of anal bleeding and are rarely dangerous, but a definite diagnosis from your doctor is essential.