With colder temperatures rapidly (unfortunately) approaching, it’s time to debunk one of the most popular myths about colds…
The color of the mucus has no bearing on whether or not sinus drainage is due to viral, allergic, or bacterial causes. The greenish color comes from an iron-containing enzyme that the body uses as a natural part of its immune system. The myth that clear mucus is viral or allergic and that yellow/green mucus is bacterial (hence requiring antibiotics) leads to the overuse of antibiotics, which can cause antibiotic resistance. Although many viral infections can lead to green mucus, if there is a lot of nasal congestion, swelling or tenderness around the face/cheek/nose or forehead or persistent cough or fever, then a bacterial sinusitis may be the culprit. But green mucus itself does not mean bacterial sinusitis. In a study of children who had yellowish/greenish mucus (cited below), the color of the mucus did not determine whether or not the child was more likely to have a bacterial infection, nor did it predict that antibiotics shorten the course of illness.
Reference: Todd, J,K,N . Todd, J. Damato, and W.A Todd. 1984 “Bacteriology and Treatment of Purulent Nasopharyngitis: A double blind, placebo controlled Evaluation.” The Pediatric Infectious Disease Journal 3 (3): 226-32.