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Mucus may be gross, but it’s vital to your health — it’s the first line of defense for your immune system.

Mucus lines the nose, throat, lungs, and digestive tract. It prevents the nose and throat lining from drying out and cracking, trapping dust, bacteria, and viruses.

Your mucus can also change color, which can give clues about a health problem. Read on to learn the reasons behind mucus colors.

Why Does Your Mucus Change Color?

When you fight an infection, like a cold or flu, your mucus color often changes. The immune system sends more white blood cells, which produce infection-fighting antibodies, to the mucus.

The color of your mucus can change for reasons other than an infection. These can include dust in the air, a nosebleed, allergies, or, rarely, lung disease.

Usually, mucus color changes are nothing to worry about, and your mucus will return to normal without treatment. But sometimes, a prolonged or unexplained mucus color change is a sign you should see a doctor.

Reasons Behind a Mucus Color

Wondering what your mucus color could signify about your health? Our phlegm color chart explains possible mucus color meaning, from clear to black.

Clear mucus

This is the color of normal, healthy mucus. But if your mucus is extra clear, it might be a sign of something. Clear mucus can signal a:

• Reaction to pollen or another allergen.
• Runny nose at the beginning of a cold.

White or grayish mucus

This color mucus can be normal, but if it’s thick, may also be an early sign of infection. When white blood cells and invader-fighting proteins flood the mucus, it can turn from clear to white.

Yellow mucus

This is usually a sign that you have a respiratory infection, whether it’s bacterial or viral. As more white blood cells build up in your mucus, it can turn from white to yellow.

If you don’t have any other cold symptoms, your pale yellow mucus could be due to allergies.

Green mucus

When you have an infection, you might notice your mucus is greenish in the morning. That’s because the white blood cells build up in the mucus overnight when you’re not blowing your nose. And white blood cells secrete a green-colored enzyme to fight off pathogens.

You may have heard that you need antibiotics if you have green mucus. While a bacterial infection can cause yellow or green mucus, a viral infection is often the culprit. If you have a virus, antibiotics won’t help, and they can lead to unwanted side effects.

“The vast majority of sinus infections are viral, which means they do not respond to antibiotics,” says Daniel Buhlinger, MD, Renaissance Family Practice-UPMC. “Although uncomfortable, symptoms generally go away on their own within 10 to 14 days.”

Pink or red mucus

Blood typically causes pink or red snot. Most often, people get blood in their mucus because the air is too dry, which irritates the nostrils and causes a slight nosebleed.

Infections or injuries can also cause blood in the mucus from your nose. Blowing your nose too aggressively can also cause a small blood vessel to burst.

In rare cases, benign (non-cancerous) or cancerous growths in the nostril can cause bloody mucus.

Note that coughing up bloody mucus is concerning and could be a sign of pneumonia, tuberculosis, or other conditions.

Brown mucus

Your mucus may be brown because it contains older blood that took time to make its way out. Or, you may have inhaled dust that turned your mucus brown. If you smoke, you may cough up brown mucus or phlegm.

Black mucus

Most often, you have black mucus from breathing in dust or pollutants. But black mucus can also be a sign of a fungal infection.

When to See a Doctor

You typically don’t need to see a doctor simply because of a change in mucus color. Most of the time, your mucus changing color is a sign that your immune system is fighting something, and you can let it do its job.

However, you should contact your doctor if:

• You have black snot coming from your nose that isn’t caused by dust or pollutants. You may have a fungal infection.
• Your mucus and respiratory symptoms don’t get better after 10 days.
• You’re coughing up greenish or yellow mucus and have other concerning symptoms, such as chest pain, rapid breathing, or shortness of breath. You could have pneumonia.
• You’re coughing up red, brown, or black mucus. This could be a sign of pneumonia or another serious lung condition.
• You’re coughing up significant amounts of mucus, even if it’s clear or white. Some lung problems, such as chronic obstructive pulmonary disease (COPD), can cause extra lung mucus.

Your Mucus Color Is Only One Clue to Your Health

Mucus color alone isn’t enough to diagnose a problem. Your doctor will also perform tests to see if you have a bacterial infection or another medical problem requiring treatment.

For example, they may do a throat swab to test for strep throat. They could also recommend a sputum test to look for bacteria or fungi in phlegm in your lungs.

What to Do If You Have Congestion

If you have a stuffy nose due to mucus, you can:

• Blow your nose — But gently, so you don’t burst a blood vessel.
• Drink plenty of fluids — Staying hydrated helps thin mucus so you don’t feel so congested.
• Run a humidifier — Moisture can break up congestion and help you breathe.
• Take over-the-counter (OTC) decongestants — Avoid using them for more than three days, as this can cause congestion to worsen when you stop using them.
• Use a nasal spray or neti pot — To avoid introducing microbes into the nasal passage, only use distilled, sterile, or boiled water in a neti pot.

Editor's Note: This video was originally published on December 27, 2022, and was last reviewed on October 8, 2025.