Why is snot green?

Answer

In addition to dead, exfoliated cells and mucus, the product “snot” often also contains bacteria (they are not the cause of colds, they only appear at the end) and dead white blood cells. They are probably responsible for the color. In a purely viral infection, the mucous secretion is much clearer.

The same difference is also seen in phlegm or sputum as a result of bronchitis. In the bacterial variant, it is often also yellow-green.