What color of sputum is generally indicative of a bacterial infection?

Yellow sputum is typically associated with a bacterial infection due to the presence of white blood cells, particularly neutrophils, that congregate at the site of infection. This yellow coloration arises from the enzymes and other substances produced by the immune response targeting the bacteria. In many respiratory conditions, yellow sputum suggests that the body is actively fighting off an infection, making it a significant clinical indicator.

While other colors of sputum can indicate various health issues, yellow sputum specifically hints at a bacterial infection scenario. Mucoid sputum is often seen in conditions such as asthma or chronic bronchitis and usually indicates a more chronic condition rather than an active infection. Green sputum can also come from bacterial infections, but it often indicates a more severe or longstanding infection, as it may contain dead bacteria and more neutrophils. Brown sputum typically signifies the presence of blood that has been altered by the lung environment, usually associated with conditions such as chronic bronchitis or certain infections but does not specifically indicate a bacterial infection.