The truth about mucus

By Stephanie Watson

WebMD Feature

Mucus is something everyone has, and some people wish they had a lot less of the stringy, gooey stuff.  Sure, it can be gross to blow globs of snot into tissue after tissue when you have a cold or sinus infection, but mucus actually serves a very important purpose.

"Mucus is incredibly important for our bodies," explains Michael M. Johns, III, MD, director of the Emory Voice Center and assistant professor of otolaryngology -- head and neck surgery at Emory University. "It is the oil in the engine. Without mucus, the engine seizes."

How much mucus is normal, and how much is too much? What does its color tell you about your health? Can you just get rid of it, or at least cut down on it, and how should you do that? Here are answers.

Mucus' Mission

Mucus-producing tissue lines the mouth, nose, sinuses, throat, lungs, and gastrointestinal tract. Mucus acts as a protective blanket over these surfaces, preventing the tissue underneath from drying out. "You have to keep them moist, otherwise they'll get dry and crack, and you'll have a chink in the armor," says Neil L. Kao, MD, associate professor of medicine at the University of South Carolina School of Medicine.

Mucus also acts as a sort of flypaper, trapping unwanted substances like bacteria and dust before they can get into the body -- particularly the sensitive airways. "You want to keep that environment, which is a sterile environment, free of gook," says Johns. "Mucus is kind of sticky and thick. It's got viscosity to it that will trap things."

But mucus is more than just sticky goo. It also contains antibodies that help the body recognize invaders like bacteria and viruses, enzymes that kill the invaders it traps, protein to make the mucus gooey and stringy and very inhospitable, and a variety of cells, among other things.

Why Am I Making So Much Mucus?

Even when you're healthy, your body is a mucus-making machine, churning out about 1 to 1.5 liters of the stuff every day. Most of that mucus trickles down your throat and you don't even notice it.

However, there are times when you do notice your mucus -- usually not because you're producing more of it, but because its consistency has changed.

"Typically, the mucus changes character. It gets thicker," Johns says. "When it has mass effect you feel it, and when you feel it, you want to hock." Some people just naturally have thicker, stickier mucus than others.

It generally takes a bad cold, allergy, or contact with something irritating -- like a plate of nuclear-hot Buffalo wings -- to throw your body's mucus production into overdrive.

For instance, during an allergic response to an offending trigger, such as pollen or ragweed, mast cells in your body squeeze out a substance called histamine, which triggers sneezing, itching, and nasal stuffiness. The tissue of the mucus membranes starts leaking fluid, and your nose begins to run.

Drinking milk may also make some people produce more mucus. Kao says that's due to gustatory rhinitis, a reflex reaction that's triggered by eating. Gustatory rhinitis is also why your nose runs when you eat hot peppers. Milk proteins cause the same type of response in some people. But although you may feel like you have more phlegm, you're not going to worsen a cold by drinking a glass of milk, Johns says.

Why Does My Mucus Change Color?

If you've ever stopped to look at the contents of the tissue after you've blown your nose, you may have noticed that your mucus isn't always perfectly clear. It may be yellow, green, or have a reddish or brownish tinge to it. What do those colors mean?

You might have heard that yellow or green mucus is a clear sign that you have an infection, but despite that common misperception, the yellow or green hue isn't due to bacteria.

When you have a cold, your immune system sends white blood cells called neutrophils rushing to the area. These cells contain a greenish-colored enzyme, and in large numbers they can turn the mucus the same color.

But "you can have perfectly clear mucus and have a terrible ear and sinus infection," Kao says. If you do have an infection, you'll likely also have other symptoms, such as congestion, fever, and pressure in your face, overlying the sinuses, Johns says.

Multi-hued mucus also relates to concentration of the mucus. Thick, gooey mucus is often greenish, Kao says.

Mucus can also contain tinges of reddish or brownish blood, especially if your nose gets dried out or irritated from too much rubbing, blowing, or picking. Most of the blood comes from the area right inside the nostril, which is where most of the blood vessels in the nose are located. A small amount of blood in your mucus isn't anything to worry about, but if you're seeing large volumes of it, call your doctor.