Causes include:
1. Perianal skin tags – these are benign. If they are causing problems(ie difficulty wiping clean after bowel action), then they can be removed
2. Haemorrhoids – especially third or fourth degree ones which prolapses out. These may be too big to band and may need formal haemorrhoidectomy
3. Perianal haematoma – this is painful and due to a ruptured blood vessel in the area causing a clot to form

4. Other Soft tissue lesions – eg cyst, lipoma, benign tumours such as hidradenoma

5. Anal cancer – this is rare, the lump is usually hard and may be associated with bleeding

6. Rectal polyp prolapsing out!

7. Rectal prolapse – this causes a large lump in the area. Surgical repair is usually indicated.

The best thing to do is to see a doctor about this and have this assessed properly.