Is it bad if your mucus is brown?

Brown phlegm can also be a warning sign because it signals prior bleeding. As the blood ages, it turns brown. If you notice brown phlegm, you should see your doctor. Black phlegm is cause for alarm—it likely signals a fungal infection, especially for people with compromised immune systems.

What infections cause brown mucus?

PID is an infection of the cervix and uterus that can sometimes result in brown discharge. It's usually caused by an untreated STI like gonorrhea or chlamydia. Other PID symptoms include pain in the lower abdomen and pelvis, pain during sex, fever, painful urination, and heavy discharge with a bad smell.