Does yellow mucus mean you need antibiotics? What phlegm can – and can’t – say about your health

When you’re sick you’ll often produce more phlegm, and might notice it’s thicker or a different colour: white, green, yellow or maybe even brown.

What can this phlegm – also called mucus, snot, sputum, catarrh and booger – really tell us about our health?

Here’s what to look for, and when to see a doctor.

What is phlegm?

We all produce mucus, even when healthy. Mucus is a barrier to the outside world that helps protect the organs in our bodies.

© La Conversation - dimanche 27 juillet 2025