Green phlegm usually means your immune system is actively fighting an infection. Most often that is a common cold or flu virus, not a bacterial one. On its own, green does not mean you need antibiotics. It typically clears in 1–2 weeks alongside the rest of a cold. What matters more than the colour is how you feel: green phlegm with a high fever, breathlessness, or symptoms lasting past three weeks is the signal to see a doctor.

A chesty cough is your body clearing mucus from the lungs and airways, usually caused by a cold, flu, or chest infection. Most chesty coughs clear in 1–3 weeks. The fastest way to feel better is to thin the mucus with hydration, steam, and an expectorant cough syrup. Avoid suppressants. They trap mucus and prolong the cough. See a doctor if the cough lasts past 3 weeks or you cough up blood.