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What causes phlegm and congestion?

Mucus—also called phlegm and snot—is essential for keeping you healthy. But too much mucus can be uncomfortable and annoying. Pratik Thaker, M.D., a Piedmont family medicine physician, explains why your body produces it and what to do if you’re congested.

Why your body produces mucus

Mucus is an important part of your overall health. The substance lines moist surfaces in your body, including your intestines, stomach, lungs, mouth, eyes and sinuses. Mucus keeps these tissues from drying out and protects them from outside materials, like bacteria, allergens, dust and viruses.

All day, you inhale bacteria into your body, which gets trapped in the mucus that lines the lungs. Then, little hairs that line your lungs—called cilia—push the mucus out of the lungs. It’ll come up your throat, and you’ll swallow it back down, usually without noticing it. From there, it’ll pass through your stomach and out of your digestive tract.

Why you have too much mucus

When you get sick, your body makes stickier, thicker mucus, which can cause uncomfortable symptoms like a stuffy nose, postnasal drip in your throat, and coughing. This is to fight the infection.

“Phlegm is a good thing because it traps potential irritants,” Dr. Thaker says.

Allergies can also cause mucus production to go into overdrive. When you have an allergy, your body will produce histamine, which can cause swelling in the mucus membranes.

What different colors of phlegm and snot mean

Mucus is normally clear, but it may become whitish or yellowish when you’re sick. Greenish, reddish or brownish snot and phlegm can sometimes, but not always, signal a bacterial infection, Dr. Thaker says.

“The main thing I’m concerned about is bloody or brown phlegm, which could be a sign of a more serious health issue,” he says.

How to relieve excess phlegm and snot

If excess phlegm or snot are making you uncomfortable, Dr. Thaker recommends these at-home remedies:

  • Use a nasal saline rinse or spray to help clear out the mucus.

  • Take over-the-counter medication, such as an expectorant, to thin mucus in your chest or a decongestant to help your body produce less mucus.

  • Place a warm, damp washcloth on your face to help relieve discomfort.

  • Temporarily use a humidifier to make the air in your home moist to help with your symptoms. Avoid overusing a humidifier, as it can grow mold, which can make symptoms worse.

  • Use a warm saltwater gargle to relieve a sore throat.

  • Stay well-hydrated by drinking plenty of water and clear fluids.  

When to see a healthcare provider

If you suspect you may have the flu, contact your primary care provider as soon as possible. They may prescribe an antiviral treatment to shorten the duration of your symptoms.

Here’s how to know the difference between the flu, COVID-19 and common cold symptoms.

If you have a common cold and symptoms last for more than two weeks, see your healthcare provider. It’s possible for a viral infection (like the common cold) to turn into a bacterial infection, which requires treatment.

“It’s possible to get a superimposed bacterial infection,” Dr. Thaker says. “When you have a viral infection [like the flu, common cold or COVID-19], your immune system can weaken, allowing a bacterial infection to develop.”

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