It's like an abscess, ie a pocket of pus, often caused by an infected hair, but I'm not sure if this is always the case. Unfortunately, they can be very painful and a little persistent in some cases. I have had more of them than I care to remember and they have been treated in a variety of ways:

- very hot baths (lots of them). I have spent many nights at 2 or 3 am in the bath, just to ease the pain;

- antibiotics (which, if you're lucky will settle them down) ;

- in extreme cases, drainage under general anaesthetic, followed by daily dressing (known as 'packing'), or insertion of a Seton loop, which is a rather strange invention, but one which is rather effective. It's a bit like a soft drinking straw, looped through the site of the infection and tied up externally. It stops the fistula from closing up and drains any pus away. It is left in until it falls out, which can be quite a long time, ie several months, but although it's uncomfortable at first, you get used to it and hardly notice it's there.

- if they are persistent you may be given other medication such as Azathioprine, but this is only really effective once it has settled down, to prevent re-occurrence.

HTH

Rebbie