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How does inflammation produce pus?

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Pathways of complement activation — inflammation The main function of complement proteins is to aid in the destruction of pathogens by piercing their outer membranes (cell lysis) or by making them more attractive to phagocytic cells such as macrophages (a process known as opsonization). Some complement components also promote inflammation by stimulating cells to release histamine and by attracting phagocytic cells to the site of infection.

Pus is produced through a process called suppuration, which occurs during an inflammatory response when the body struggles to eliminate an infectious agent, such as pyogenic bacteria like Staphylococcus or Streptococcus.1

As part of the body's defense mechanism, white blood cells—specifically neutrophils—migrate to the site of injury or infection to ingest bacteria and clean up cellular debris through phagocytosis. Pus forms as a thick, opaque, yellowish-white fluid composed of:2345

Degenerating or dead white blood cells (leukocytes)
Dead or living microorganisms (bacteria)
Tissue debris
Extracellular fluid leaked from blood vessels31

When this accumulation of pus becomes localized within a cavity formed by broken-down tissue, it is known as an abscess. In this state, the body may attempt to wall off the infection by forming a capsule of tissue around the pus to delimit it from surrounding healthy areas.31