Understanding Pus: Composition, Causes & What It Means for Your Health

Pus (purulent exudate) is a thick, yellow-white fluid signaling active infection.

Composition

• Dead neutrophils (primary component) – sacrificed in phagocytosis.
• Bacteria (live and dead) – the infectious agents.
• Tissue debris – necrotic cells, fibrin.
• Serum proteins – edema fluid, immunoglobulins.
• Macrophages – later cleanup.

Color & Consistency Clues

• Yellow/cream: Typical bacterial (Staph, Strep).
• Green: Pseudomonas (pyocyanin pigment).
• Brown/foul: Anaerobes, mixed flora, necrotizing infection.
• Thin/serous: Early or viral.
• Thick/creamy: Established bacterial abscess.

Clinical Significance

• Abscess = walled-off pus collection → needs incision & drainage (I&D) + culture.
• Cellulitis = spreading infection without discrete pus → antibiotics.
• Sterile pus = rare (e.g., gout, Behçet's); culture-negative.

Never ignore pus. It indicates infection requiring source control ± antibiotics.