What does the color of your mucus mean?

Mucus isn't exactly something people give much thought to — until they're sick and dealing with a constantly runny nose.

But mucus is actually an important part of a healthy immune system, according to Dr. Shawn Nasseri, an otolaryngologist who specializes in ear, nose and throat surgery. Even when you're not sick, your body produces mucus to keep tissues hydrated and prevent them from drying out. "Mucus, along with the respiratory tract and the upper digestive tract, act in many ways as the lubrication, filter and protection for our bodies," he tells Yahoo Life.

Nasseri adds: "Every day our bodies produce approximately 1 liter of mucus in the nose and double that amount in the throat!"

So what, exactly is mucus?

Also known as phlegm, mucus is made up of mostly water, but it also contains "remnants of skin-lining cells (epithelial cells), antimicrobial enzymes, proteins and inorganic salts," explains Nasseri. "It is produced by your mucous membranes and coats your mouth, nose, sinuses, throat, lungs and gastrointestinal tract."

Mucus is actually the body's first line of defense against bacterial and viral infections. One of the proteins found in mucus — the antibody IgA — protects against pathogens in your nose and mouth, notes Nasseri. "Normal healthy mucus travels in a pattern from the front of the nose to the throat by a special way called mucus transport (mucociliary transport), through tiny hairs pushing it along the nose and down the throat," explains Nasseri. "IgA, along with other proteins that slow or prevent bacterial, fungal and viral growth, work to keep the lining healthy and working at its peak efficiency."

Nasseri adds: "This function keeps unwanted pathogens from entering the body and supports our immune system."

Why mucus production steps up when you're sick

When you get sick, have allergies or even just have irritants such as dust in your nose and throat, the respiratory tract "kicks into high gear to protect us," says Nasseri. This includes "white blood cells to fight infection, increased proteins that cause inflammation and more sloughing of the skin-lining cells… which tend to stick together and clump," he says.

This causes the mucus to get thicker and more difficult to clear. It can also cause a cascade that includes releasing "histamine and other secondary proteins to make the nose or throat swollen and feel stuffy, painful or sick," says Nasseri.

In other words, "your body is responding to some sort of irritant and is creating the mucus to combat the issue," Dr. Jonathan Parsons, a pulmonologist at The Ohio State University Wexner Medical Center and director of Ohio State’s Asthma Center, tells Yahoo Life. "It can be related to a bacterial infection like bronchitis, sinusitis or pneumonia. It could be a viral infection like your regular, run-of-the-mill upper respiratory infection. It can be produced by people who have chronic lung disease like COPD, cystic fibrosis or bronchiectasis. It's a part of environmental allergies and asthma as well."

What does the color of your mucus mean?

Mucus is typically clear and thin, but it can change color and consistency, depending on your health.

If your mucus is yellowish…

Yellowish mucus typically means that your white blood cells are "fighting off an illness or infection," says Nasseri. "Most commonly this is linked to the common cold and will likely clear on its own. So long as it is only yellow for less than a week to 10 days, it usually means your body is fighting off normal infection."

If yellow mucus is accompanied by fever, chills, muscle aches or pain, Parsons recommends letting your primary care provider know and sharing how long you've been sick. "This will help your doctor determine if you need antibiotics or if it's something they can watch for a little longer and see if you can make it through without antibiotics," Parsons says.

If your mucus is greenish…

"Bacterial infections such as sinusitis caused by common bacteria like strep pneumonia, moraxella, haemophilus and staph aureus and other upper respiratory infections can cause green mucus," Nasseri says.

Greenish mucus "means that your body is fighting off an infection and the white blood cells/proteins are kicking into high gear," explains Nasseri. "You will likely have other systems such as fever, congestion and sinus pressure."

If it doesn't clear up after 10-12 days, you have severe symptoms, or a fever above 101.5 degrees, Nasseri suggests consulting your health care provider.

If your mucus is reddish…

"When blood is mixed in the mucus [from the nose] it is likely from nasal irritation or a dry climate," explains Nasseri. "I would recommend using a sterile saline spray two to three times daily to keep the mucous membrane moist and lubricated."

Nasseri also recommends avoiding picking at or further irritating the nose. "Try not to blow the nose very hard or scratch/irritate the inside, as that is usually where the blood is from," he says.

However, if it persists, you should see your doctor. In addition, "if you're coughing up red, pink or bloody phlegm or mucus, you should be seen by your health care provider because this could be related to an infection or even to cancer in some cases," says Parsons. "If you're a smoker and you’re coughing up blood, it is worrisome. Your doctor may take a more in-depth health history and order a chest X-ray before making a diagnosis."

If your mucus is brown or black…

A fungal infection or polluted air can cause brown or black mucus, according to Nasseri.

"Charcoal or sooty looking phlegm is often seen in people who work in coal mines and factories, or are really heavy smokers," says Parsons. "If you work in a factory where there's a ton of smoke and don't wear a mask, you’re inhaling all that in and it’s causing an inflammatory reaction in your airways that produces phlegm. The irritants are mixed in with the phlegm and when you cough, it comes out."

The same thing happens with cigarette smoking. "Sometimes we see patients who are smoking two to three packs a day who have a productive cough," says Parsons. "A lot of times they'll have a little bit of gray or smoky tinge to their phlegm because of the smoking."

If you have symptoms of an infection, such as a fungal infection, your doctor may prescribe both antibiotics and some steroids to reduce the inflammation. In the case of occupational exposure, doctors would recommend that you wear the appropriate personal protective equipment, notes Parsons, and quit smoking if you do light up.

Sometimes people who have significant chronic lung disease can also cough up a brownish phlegm. "Dark brown, tenacious phlegm is seen in patients who have cystic fibrosis or bronchiectasis, which is a chronic lung disease," explains Parsons. "The phlegm is brown because of blood and the intense chronic inflammation that comes with the chronic disease state. The bacteria camp out inside the lungs and cause very gradual changes in the consistency and appearance of phlegm."

If you have chronic lung disease, you may be used to seeing brown phlegm, notes Parsons. But if the health condition is exacerbated, you may require antibiotics.

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