Perianal Abscess and Fistula
Blockage of a mucus-secreting anal gland lets bacteria multiply into a walled-off abscess, and if that pus tracks a path to the skin before it is drained, the epithelialised tunnel it leaves behind becomes a persistent fistula-in-ano.
First principles
It starts with a blocked anal gland, not the skin
Small mucus-secreting glands sit in the intersphincteric space and drain into the anal crypts at the dentate line. When a duct becomes obstructed (by debris, oedema or trauma), the gland's secretions cannot escape, bacteria proliferate within the stagnant fluid, and a cryptoglandular abscess forms. This cryptoglandular origin explains why perianal sepsis begins deep, between the sphincters, rather than as a simple skin infection, and why the anatomical route the pus subsequently takes determines everything that follows.
Educational content pending clinical review. Not medical advice.