A lot of people think yellow or green snot means you need an antibiotic. That is not true. Laura Martin, MD, MPH If it's a viral infection causing the yellow or green snot, yellow in particular is ...

If your mucus is gray or black... …you likely inhaled dark-colored particles, like smoke from a fire or heavy exhaust.

“The potential causes of yellow mucus include the common cold or a bacterial infection such as sinusitis (a sinus infection) or bronchitis (a respiratory infection).” According to Connor, green mucus ...