What is a common cause of purulent sputum?

Purulent sputum, which is characterized by its thick, yellowish or greenish appearance, is commonly associated with infections in the respiratory system. When the body fights off an infection—such as pneumonia, bronchitis, or a lung abscess—it produces white blood cells and debris that contribute to the thickness and color of the sputum. The presence of pus, which includes dead cells, indicates that the immune system is actively responding to pathogens, making infection the most significant factor leading to purulent sputum.

While dehydration can affect mucus production and can lead to thicker sputum, it doesn't specifically cause the purulent characteristics that indicate infection. Allergic reactions typically result in clear or watery sputum rather than purulent fluid. Smoking may lead to chronic bronchitis or other respiratory issues, resulting in sputum production, but the sputum from chronic bronchitis often does not have purulent characteristics unless there is an accompanying infection. Thus, infection is the primary cause of purulent sputum.