Piles are swellings on the inside of the anal canal, the short, muscular tube that connects the rectum (back passage) with the anus, in areas known as the anal cushions. They are round swellings that can reach the size of a grape. Piles are not varicose veins.

Although piles develop from inside the anal canal, they can hang down out of their normal place. Piles can be described as follows.

• First degree piles are swellings on the inside lining of the anal canal. They bleed but can't be seen from outside the anus.
• Second degree piles are larger and stick out (or prolapse) from the anus when you open your bowels, but return on their own afterwards.
• Third degree piles are similar, but hang out from the anus and only return inside when pushed back in.
• Fourth degree piles permanently hang down from the anus and you can't push them back inside. They may become extremely swollen and painful if the blood in them clots.

Swellings that develop from below the anal cushions are sometimes called external piles. They can be more painful than the other types of piles. Other causes of lumps around the anus can include a "sentinel pile", which is the painless skin tag that develops when a crack in the anus (an anal fissure) heals up. Also, a collection of blood under the skin, called a peri-anal haematoma, may also be referred to as a type of external pile. The treatment of these conditions is different from true piles.

Swellings that develop from below the anal cushions are sometimes called external piles. They can be more painful than the other types of piles. Other causes of lumps around the anus can include a "sentinel pile", which is the painless skin tag that develops when a crack in the anus (an anal fissure) heals up. Also, a collection of blood under the skin, called a peri-anal haematoma, may also be referred to as a type of external pile. The treatment of these conditions is different from true piles.

Common symptoms of piles include:

• bright red blood from your anus, which you may notice on the toilet paper when wiping, or in the toilet bowl a lump on the anus
• pain and discomfort after you have opened your bowels
• a slimy discharge of mucus, which may cause itching
• a feeling that your bowels haven't emptied completely
• soiling underwear (with third or fourth degree piles)

Bright red blood from the anus is most likely to come from piles, rather than anything more serious. However, if you are unsure whether the bleeding is due to piles, you should visit your GP for advice.

The exact cause of piles isn't known. One theory is that it's due to weakness of the tissue that connects the anal cushions to the muscle layers underneath. Due to this weakness, the anal cushions slide out of their normal place and down the back passage.

You have an increased risk of getting piles if you:

• strain to empty your bowels (eg if you have constipation)
• eat a low-fibre diet
• have long-lasting (chronic) diarrhoea
• are pregnant - due to the effect of hormones on the blood vessels, plus the increasing weight of the baby within your abdomen
• have a family history of piles
• have cancer or growths in your pelvis or bowel, which may put pressure on your abdomen