Haemorrhoids are swellings that can occur in the anus and lower rectum (back passage).
There is a network of small veins (blood vessels) within the inside
lining of the anus and lower rectum. These veins sometimes become wider
and engorged with more blood than usual. These engorged veins and the
overlying tissue may then form into one or more small swellings called
The exact reason
why these changes occur and lead to haemorrhoids forming is not clear.
Some haemorrhoids seem to develop for no apparent reason. However, it is
thought that the pressure in and around the anus can be a major factor
in many cases. If the pressure in and around the anus is increased, then
it is thought that this can lead to haemorrhoids developing.
Certain situations increase the chance of haemorrhoids developing:
Constipation- passing large stools (faeces), and straining at the
toilet. These increase the pressure in and around the veins in the anus
and seem to be a common reason for haemorrhoids to develop.
Pregnancy- Haemorrhoids are common during pregnancy. This is probably
due to pressure effects of the baby lying above the rectum and anus, and
the affect that the change in hormones during pregnancy can have on the
Ageing- The tissues in the lining of the anus may become less supportive as we get older.
Hereditary factors- Some people may inherit a weakness of the wall of the veins in the anal region.