Which sputum color most commonly indicates infection?

• A. Yellow or green sputum.
• B. Clear = normal mucus or allergies
• C. White = asthma, COPD
• D. Red or pink = blood

Answer: (A)

Sputum color often mirrors the body's immune response in the airways. Yellow or green sputum is most commonly linked to infection because white blood cells, especially neutrophils, rush into the airways to fight bacteria, and the enzymes and pigments they release color the mucus as it becomes purulent. This change often accompanies bacterial involvement, though viral infections can sometimes cause similar color changes too.

In contrast, clear mucus is typical of normal mucus production or allergies, white mucus can occur with chronic airway inflammation such as asthma or COPD, and red or pink sputum suggests the presence of blood and should prompt careful evaluation.

Color alone isn’t diagnostic; always consider accompanying symptoms, duration, fever, and other clinical signs to assess infection risk.