A runny or stuffed-up nose is a pain, but that extra mucus helps your body stay healthy.

“Mucus is an important substance the body produces to protect itself from viruses and bacteria,” says Philip Chen, MD, an ear, nose, and throat doctor at the UT Health San Antonio. “It’s sticky and traps foreign particles, which the body can then sweep out like a broom.”

It also has special proteins and antibodies that fight off germs.

Your body makes a lot of this sticky goo, even when you’re not sick. Mucus keeps parts of your body from drying out. It’s in your mouth, nose, and sinuses. It also lines many of your tissues.

“We produce 1 to 1.5 liters of mucus a day,” Chen says. “Much of it is swallowed and we don't even know it.”

But when you aren’t feeling well, your mucus becomes a lot more noticeable.