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DEAR MAYO CLINIC: My grandson frequently has a runny nose, and the color of the nasal mucus is sometimes green to yellowish. I’ve heard that this is a sign of a bacterial infection and perhaps the need for antibiotics. Can you confirm?
ANSWER: Greenish-gray or yellowish nasal mucus — your health care provider might call it purulent nasal discharge — isn’t a sure sign of a bacterial infection, although that is a common myth — even in the medical world. Both viral and bacterial upper respiratory infections can cause similar changes to the type and coloration of nasal mucus.
During a common cold, nasal mucus may start out watery and clear, then become progressively thicker and more opaque, taking on a yellow or green tinge. This coloration is likely due to an increase in the number of certain immune system cells, or an increase in the enzymes these cells produce. Over the next few days, the discharge tends to clear up or dry up.
Viruses cause the vast majority of colds in both children and adults. Antibiotics do nothing against viruses — regardless of whether green mucus is produced. However, the timing of symptoms may offer a clue as to the type of germs present. Thick, colored nasal mucus more often occurs at the beginning of a bacterial illness, rather than several days into it, as occurs with a viral infection. In addition, symptoms due to a bacterial infection often last more than 10 days without improvement.
In a few cases, a bacterial infection may develop on top of a viral cold, in which case symptoms may get better and then worse again. Under these circumstances, an antibiotic may lessen the severity of symptoms and shorten the duration of the illness.
In the meantime, measures that might help include taking in plenty of fluids to stay hydrated, gently suctioning out the discharge, using saline nasal drops to rinse out or irrigate the nasal cavities, and perhaps using a cool-mist humidifier to moisten the air. (adapted from Mayo Clinic Health Letter) — Dr. James Steckelberg, Infectious Diseases, Mayo Clinic, Rochester, Minnesota