Green Snot Doesn't Mean You Need Antibiotics
Many people see green mucus as proof of an infection that needs treating. The colour comes from your own immune cells, and it says little about bacteria.
Would antibiotics help a cough clear up faster? In research reported by Public Health England in 2013, when the phlegm was green, 40% of people said yes. When it was clear, only 6% did. The colour feels like proof of an infection that needs treating. It isn’t.
Where the green comes from
Snot and phlegm of any colour are part of the body’s defences: they trap dirt, pollen and microbes. When you are fighting an infection, white blood cells gather in the area, and some of them contain a green protein. The more of these cells there are, the greener the mucus turns.
So the colour mostly shows your immune system at work. It says little about what it is fighting.
Colds are viruses
Colds, flu and most coughs are caused by viruses. Antibiotics only work against bacteria, so they do nothing for a cold, however green the mucus. The NHS says most people start to feel better in about one to two weeks.
What the evidence shows
In a German study published in 2009, family doctors at 42 practices in Düsseldorf sent sputum samples from 241 patients with an acute cough for testing. Only 28 of them, 12%, showed a bacterial infection.
Yellow or green sputum turned up in about four in five of the bacterial cases, but also in more than half of the patients with no bacterial infection. As a test, colour barely shifted the odds. The researchers concluded that for people without a chronic lung disease, sputum colour should not decide whether antibiotics are prescribed.
Why it matters
Antibiotics you don’t need won’t make you better faster, and they can cause side effects. Every unnecessary course also adds to antibiotic resistance: the more these drugs are used, the less well they work when someone really needs them.
The exception
Colour is not meaningless for everyone. Public Health England advises people with chronic obstructive pulmonary disease (COPD) to see a doctor if their phlegm turns green, because in that group it is more likely to signal an infection. The NHS also says to see a GP if a high temperature lasts more than three days, symptoms get worse, or you feel short of breath.
The takeaway
Green snot is a sign that your body is fighting something, not a sign that you need antibiotics. Judge a cold by how long it lasts and how you feel, not by the colour of the tissue.
Sources & further reading
- 01Public Health England (2013). Green phlegm and snot not always a sign of an infection needing antibiotics. GOV.UK.
- 02Altiner, A. et al. (2009). Sputum colour for diagnosis of a bacterial infection in patients with acute cough. Scandinavian Journal of Primary Health Care, 27(2), 70–73.
- 03NHS. Common cold.
- 04NHS. Antibiotics, and Antibiotic resistance.
