Mucus, a fluid in your upper respiratory system, is usually clear. But a number of health conditions can cause it to turn brown. Also known as brown phlegm or sputum, brown mucus can be due to a range ...

When you're sick you'll often produce more phlegm, and might notice it's thicker or a different color: white, green, yellow or maybe even brown. We all produce mucus, even when healthy. Mucus is a ...