Today’s article may gross some people out, but the functions of our bodies can often be gross. With that said, we’re going to talk about mucus — specifically, how the color of your mucus can give you an idea of your health. There can be value in taking note of this often-overlooked health sign. We’re not suggesting you check your phlegm every time you sneeze or cough, but glancing at it if you’re feeling unwell might help you figure out if you’re just feeling off or if you have an infection.

What Is Mucus?

The reason mucus can show what’s going on inside your body is because of what it is. Mucus is viscous substance that lines many of the tissues and internal surfaces of our bodies (e.g., our nose and lungs). It’s also called phlegm, though, technically, phlegm refers to mucus created specifically by the respiratory system. Anyways, mucus plays an important role in our health. It’s an integral part of our immune system, trapping pathogens before they can become a problem. Mucus also contains antibodies and enzymes that aid the immune system by killing the trapped pathogens before ushering them out of your body with a well-timed cough or sneeze. In a sense, mucus is the bouncer of your body.

What the Color Means

You may have heard someone tell you that green mucus means a bacterial infection and yellow means viral, but this is actually a myth. The color of your mucus doesn’t tell you the type of illness you have. It can be useful in telling you if you’re sick or how severe of a reaction you’re having. Generally, the color of your mucus refers to a reaction in your immune system. Normally, mucus is fairly clear, so when there’s a color to it, that means there’s something else there. Most of the time, this “something” is white blood cells acting as part of your immune system. The more vibrant the color your mucus, the more white blood cells that are in it, usually; that’s not always the case.

Cloudy or Milky

When you see cloudy mucus, this usually means a very mild infection or even seasonal allergies. This is due to the small number of white blood cells in the mucus. This is likely nothing to worry about, though worth keeping an eye on if it develops further.

Yellow or Green

If the mucus takes on a yellowish or greenish color, it often points toward an infection (though it may just be the result of an irritant). While this can occur from a buildup of white blood cells overnight, when you have seasonal allergies, it’s more common when you have a cold or infection. The reason it turns a yellow or greenish color is due to the white blood cells, specifically neutrophils. These cells contain a greenish-colored enzyme that colors your mucus in high concentrations. So, when it’s yellow, you’re dealing with a mild infection. The greener the mucus gets, the more severe the infection likely is, because your immune system is working harder to get it under control. You likely don’t need to rush to the doctor but bringing this up to your primary care physician wouldn’t hurt.

Brown or Red

Now this grouping has nothing to do with your immune system. If your mucus is brown or red, it tells us that there’s blood in your mucus — the brighter and redder the color, the fresher the blood. Depending on where the blood is coming from, this can mean a few things. If the mucus is coming from your nose or sinuses, it can be from trauma to your skin tissue, from blowing or sneezing too hard and tearing in the skin, or from dryness causing cracks in the skin. If the brown or red mucus is coming from a cough, that means the blood is in your lungs or airways. This can be more severe. The most common explanation is prolonged coughing causing tears or a chest infection. It can also be much more dangerous. If you’re finding brown or red mucus in your coughs, you should see a doctor to ensure it’s not something more severe.

Black

The most concerning of all the colors of the mucus rainbow, black-colored mucus points to two things. The less worrisome explanation of the two is the presence of pollutants, specifically smoke. If you smoke or recently were in close vicinity of a large fire, the smoke can pollute your mucus. Even if you suspect that this is the cause, you should still see the doctor, because the other reason is a severe infection. This can be a fungal infection, tuberculosis, or even lung cancer. Each of those conditions are dangerous and need treatment immediately. If you’re coughing up black mucus, see your doctor immediately.

● ● ●

While the color of your mucus won’t tell you whether you need antibiotics or antiviral medications, you can use it as a nice way to gauge the severity of an illness or symptoms. It’s important to remember that the color of your mucus only provides general signs of your health. If your mucus is lightly cloudy, but you feel horrible or your symptoms have stuck around for a while, it’s still worth going to the doctor.