What it means
An abscess is a collection of pus enclosed within a capsule of inflamed tissue. Pus consists of dead white cells, bacteria and tissue debris.
The capsule that contains the infection also protects it: blood supply to the centre of an abscess is poor, so antibiotics penetrate it badly.
This is the central practical fact about abscesses — ubi pus, ibi evacua, where there is pus, drain it. Antibiotics alone frequently fail.
In practice
Occurs anywhere: skin, dental, breast, perianal, tonsillar (quinsy), and within organs such as the liver or lung.
A fluctuant swelling on examination is one that feels fluid-filled, indicating a drainable collection.
Why it matters
An abscess usually requires drainage, either by incision or by needle aspiration under imaging guidance. Antibiotics are given alongside rather than instead.
A rapidly enlarging, very painful abscess with fever, or one on the face near the eye, requires urgent assessment. Perianal abscesses in particular should not be left to settle.
Clinically reviewed by Dr Mohammad Zubair Khan, GMC 7563469
Last reviewed
August 30, 2026