They are capillaries (like small veins) which are cushions that help with controlling your poo.

They can become swollen, which is a disease, also called Hemorrhoids after the structures in your anus.

The swollen hemorrhoids can be either insane or outside of your butthole.

When they are internal, you can get bright red blood in your poo, but no pain.

When they are external pain and swelling is noticeable around your butthole. This can make sitting down uncomfortable to painful. External ones don't usually bleed, but can. When they heal, they can leave behind skin tags.

Constipation, sitting on the toilet too long, and diarrhoea are common causes. Also pressure in the abdomen causes them, so they are very common in pregnant women.

Normally no treatment is needed and they will clear up in a few days. Drinking plenty of water and eating plenty of fibre will be useful. In extreme cases, medications and even surgery may be necessary to resolve them.