Cold and flu season is here, and you might already be reaching for tissues. But before you toss that tissue, take a quick look at the mucus color—it might tell you more than you think.

We asked Mbuyi Kalemba, PA-C, a family medicine physician assistant at Hartford HealthCare, to explain what different mucus colors could mean and when to talk to your doctor. Here’s what you need to know.

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What is mucus, and why does our body produce it?

Mucus is a glue-like fluid produced by mucous membranes and glands, made up of mucin, leukocytes, inorganic salts, water and epithelial cells.

In short — it’s a good thing.

“The body produces mucus to keep tissues lubricated and to trap irritants and foreign materials,” says Kalemba. “It also plays an important role in the immune system.”

When healthy mucus does its job well, it’s usually clear, thin, and watery (or white)—signs of adequate hydration.

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What does your mucus color say about your health?

When your usually clear mucus changes color, it might signal what’s happening inside your body.

With insights from Kalemba, here’s a quick look at what different mucus colors could mean:

  • Yellow or green: Often normal, yellow can hint at inflammation or infection, while green may point to a cold or a viral or bacterial infection like a sinus infection or bronchitis.
  • White or cloudy: While white is typically normal, cloudy mucus may be normal or indicate inflammation.
  • Red or pink (blood-tinged): If it’s from the nose, it could be irritation from frequent nose blowing or picking, but could also indicate other sources of bleeding. When it comes from the lungs, red mucus may suggest irritation, bleeding, infection or possible cancer.
  • Brown or black: May indicate old blood or result from inhaling smoke or soot, especially after exposure to a fire.
  • Pink and frothy: This may indicate pulmonary edema or heart failure. If mucus is consistently pink or red with a foamy texture and is accompanied by symptoms like cough, fever or chills, seek immediate medical attention.

> Related: 5 Health Conditions That May Run in Your Family

See your doctor instead of self-diagnosing.

If your mucus isn’t clear and watery and has a consistent color change, it’s a good idea to check in with your doctor.

“Mucus can hint at an infection or other health issues, but it’s not always a clear indicator,” says Kalemba. “We look at mucus color alongside other symptoms to understand what’s going on. So, if your mucus color has changed and you’re concerned, schedule an appointment to get it checked out.”