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What Are the Most Common Causes of Brown Phlegm?

By Christina Edwards
Updated Mar 03, 2024
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The most common causes of brown phlegm are smoking and exposure to second-hand smoke; a number of other environmental issues like air pollution and dust may also be to blame. Sometimes a person’s diet could trigger the production of phlegm as well. In more serious cases the root cause could be a respiratory infection or lung problem, though in these instances the phlegm tends to be on-going, which means that it doesn’t go away on its own — and in fact may actually get worse as time goes by. People are often alarmed when they first start coughing up brown phlegm, but it’s rarely anything to worry about. Just the same, anyone who is worried about their condition, particularly if the phlegm is accompanied by other symptoms like wheezing or fever, should usually get the advice of a qualified medical provider.

Understanding Phlegm

Phlegm is a thick, tacky substance that is sometimes expelled out of the body through coughing. It can come in a number of colors, such as white, yellow, green, and brown. It’s really similar to mucus, and in fact many experts say that the two substances are biologically identical. The difference in title is often related to where in the body each occurs, rather than primary function. On this understanding, phlegm is mucus that occurs in the respiratory tract, and is usually triggered by some sort of irritant.

Some mucus or phlegm is almost always in the throat and lungs, and is one of the main ways the body moves foreign particles like dust through the lungs. Small particles are often inhaled by accident, and moving them out is a relatively easy way for the body to maintain its efficiency. The lung’s cilia, which are cells that line the lung walls, are where the mucus is produced. These contain hair-like protrusions that essentially act to “sweep” the particles away.

People don’t usually notice their phlegm or know what color it is until there’s so much of it that the body needs to expel some. When something triggers an increased production, people often find themselves coughing up or spitting up phlegm. A brown color is usually considered unusual, though there are many possible explanations.

Concerns for Smokers

Smoking is one of the most common causes of brown-colored phlegm. When people regularly intake the smoke from cigarettes, cigars, or pipes, in most cases they’re breathing in more than just nicotine smoke — they’re also getting a range of resins, tars, and other chemicals. These tend to become trapped in the lungs. Heavy smokers will often cough up a small quantity of brown mucus, especially in the morning, and in most cases this is just a normal part of the lungs trying to clean themselves and expel the foreign particulates.

Individuals who are trying to quit smoking may also find themselves coughing up large quantities of brown phlegm. After a person quits, the cilia in the lungs, which have often been damaged or at least slowed by smoking, begin to work at a fuller potential again. These tiny hair-like projections then begin to sweep out the large quantities of phlegm caught in the lungs. This process can last for months in some individuals.

Environmental Exposure

People who live in areas with very polluted air might also cough up brownish phlegm from time to time. Dust and dirt can also be a cause. When cleaning a dusty room or working around blowing sand or dirt, tiny particles can get caught in the throat. This mucus will then be coughed up, and the resulting phlegm will appear brown and grainy. In nearly all cases this is a temporary condition, and will go away as soon as the exposure has stopped.

Food and Drinks

Certain foods and drinks can cause a person's phlegm to appear brown. This is usually harmless, although it can be worrisome. Chocolate, red wine, and dark sodas can all temporarily alter the color of a person’s phlegm.

Infections and Health Problems

Certain respiratory or lung infections are more serious causes. Usually when a person gets a respiratory illness, the lungs will begin to produce more mucus than normal to trap certain bacteria and other foreign matter. Brown phlegm is a common sign of chronic bronchitis, for instance, and more serious respiratory infections, such as lung cancer or emphysema, might also be present.

A lot of things can possibly contribute, but getting to the root of the exact cause almost always requires an exam by a qualified medical expert. Anyone who is worried about the phlegm they’re coughing up, particularly if the problem has been going on for some time, is usually advised to get a medical check-up just to rule out more serious conditions.

How Long Will Brown Phlegm Last?

The duration of brown phlegm varies depending on the type of phlegm and what is causing it. For example, brown phlegm caused by something food-related or diet-related will likely last for a shorter time than brown phlegm caused by a chronic condition. 

Chronic conditions such as COPD, Cystic Fibrosis, or lung disease will all cause sticky, brown phlegm that will likely hang around for an extended period. In some cases, such as asthma, the brown phlegm will not go away until the condition is adequately treated. 

For a short-term condition, such as brown phlegm caused by eating a particular type of food, you can expect it to last no more than a few days. On the other hand, suppose a chronic condition causes the brown phlegm. In that case, however, you may be plagued with it for anywhere between 10-14 days or longer. 

What Are Some Chronic Conditions that Produce Brown Phlegm?

Various chronic conditions can be the root cause of brown phlegm. If your brown phlegm is consistent and does not clear on its own within a few days, consult your doctor to ensure you are not experiencing one of these significant chronic conditions. 


Bronchiectasisis a condition that results in excess mucus being built up in the lower part of the lungs. This unwanted side effect is caused by the airways that are conjoining to the windpipe at the lower part of the lungs being too widespread. The spare room in the lungs is an excellent place for the mucus to inhabit. Therefore, it builds until, eventually, it could become a problem, and brown phlegm may form.

Cystic Fibrosis

Cystic Fibrosis is a disorder in which the body cannot secret normal mucus. The primary purpose of mucus within the body is to provide a secretion that is slippery and moist, which is how it does its job: to excrete unwanted or unnecessary particles out of the body. 

Someone suffering from Cystic Fibrosis would not be able to produce mucus properly; therefore, the mucus becomes thick and sticky, making it hard to excrete toxins without getting stuck. 

This thick and sticky mucus then becomes a problem and can cause the passageways to the lungs and pancreas to become blocked. In addition, as the mucus sits in the lungs for an extended time, brown phlegm can form. 

Brown phlegm caused by Cystic Fibrosis should never be ignored. 

Bacterial Pneumonia

Bacterial pneumonia is an infection in which bacteria begin to invade the lungs. A common cause for this condition is a case of bronchitis not treated quickly enough. Brown phlegm is most often associated with bacterial pneumonia and is often one of its most common symptoms. 

What Other Conditions Can Cause Brown Phlegm?

Aside from chronic conditions, brown phlegm may also be caused by something less concerning, such as an infection or allergy. For example, experiencing an allergic reaction to Fungus is one non-chronic reason that could explain your brown phlegm.

A lung abscess is another example of an infection that would produce brown phlegm. A lung abscess, although not life-threatening, can be a very serious condition and, when accompanied by brown phlegm, should always be diagnosed and treated promptly. 

Brown Phlegm Caused by Fungus

Brown phlegm may result from someone experiencing an allergic reaction to the common Fungus, aspergillus. Aspergillus is produced by wilting plants, soil, and natural vegetation. Some people become slightly allergic to this Fungus, and thus brown phlegm may result from that. 

The good news is that if a fungus allergy causes your brown phlegm, your doctor can treat that reasonably quickly by prescribing anti-inflammatory medication. 

Brown Phlegm Caused by a Lung Abscess

A lung abscess is another infection that can cause someone to cough up brown phlegm. A lung abscess is when the lung tissue starts to break down, and cavities form within the lung tissue. These cavities trap and hold onto fluid and debris, thus causing an infection. 

When a lung abscess festers for too long, that is when you start to cough up this excess fluid and brown phlegm, which is an indicator that bacteria and blood are present in the lungs. 

Again, since the brown phlegm caused by a lung abscess is bacterial, it can be quickly and easily treated using antibiotics and anti-inflammatory drugs.

The Health Board is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.

Discussion Comments

By kylee07drg — On Jul 31, 2011

After years of smoking and chewing tobacco, my grandfather developed emphysema. Though he lived into his eighties, he suffered a good deal while trying to breathe.

He kept a jar by his recliner into which he spit the brown phlegm that he coughed up on a regular basis. His voice had become hoarse and weak from all of the coughing, and it really tired his whole body out.

I always had a sense of doom when I went to see him. That rattling cough and the resulting dark phlegm told me that he wouldn’t last much longer on this earth.

By OeKc05 — On Jul 31, 2011

When my husband and I rented our first house, we had to go in and do some major cleaning to get it ready. One super dusty area we had to tackle was the utility room attached to the garage where our washer and dryer would go. Since it was outdoors, it had layers of dirt built up on the shelves and tons of cobwebs in corners.

Had I known what it would do to me, I would have worn a mask while cleaning it. We stirred up the dust and dirt into the air, and we breathed it in. Immediately, I began coughing. By the next day, I was hacking up brown phlegm. I developed an infection that required antibiotics, and the brown phlegm persisted for a couple of weeks.

By Oceana — On Jul 30, 2011

I never knew that what I ate and drank could colorize my phlegm. I guess I just assumed that since food goes through the digestive system and phlegm goes through the respiratory system that the two never met.

I do drink dark sodas, and I eat a substantial amount of chocolate. So, when I got bronchitis, which already makes you have brown phlegm, mine was extra brown. It freaked me out when I first saw it, because I thought it might have dried blood in it.

My doctor reassured me that the color of my phlegm was normal for someone with my diet and disease. I felt better knowing that I was not bleeding internally!

By shell4life — On Jul 29, 2011

My husband recently got an upper respiratory infection. He began coughing up brown phlegm. He thought he had strep throat because it hurt so much to swallow, but the nurse practitioner told him it was a different kind of infection.

I’m sure his phlegm was even browner than that of most people who get respiratory infections, because he is a smoker. The nurse practitioner told him he really needs to quit, because smoking is an irritant. It takes him longer to recover from respiratory illnesses because of his smoking habit. He will be coughing up brown phlegm for longer than normal after the infection leaves his body.

By JessicaLynn — On Jul 28, 2011

@janeAir - My mom used to ask us that too when we were kids. She always wanted to make sure our phlegm wasn't green, because that means infection.

It sounds like in some cases, brown phlegm is worse than green. I think I would definitely rather have some type of infection than lung cancer or emphysema.

By JaneAir — On Jul 28, 2011

When I was younger, whenever I had a cough my mom would always ask me what color my phlegm was if I was coughing any up. I always thought this was really gross!

However, as usual, mother knows best. Like the article said, the color of the phlegm can tell you a lot about what is wrong. For example, one of my great aunts had lung cancer. One of the first symptoms she showed was coughing up brown phlegm.

By manykitties2 — On Jul 28, 2011

@lonelygod - Even if your mother doesn't have lung cancer it certainly sounds like something more is going on than just a regular smoker's cough. My grandmother had the same thing and she found herself constantly getting lung infections like bronchitis.

If your mother thinks that something is wrong it is really best that you make sure she sees a doctor. Smoking can have a lot of negative long term health effects, but that doesn't mean she shouldn't still see the doctor when her brown phlegm gets worse. It really is better to be safe than sorry. If it is just from her smoking, so be it. But I think your whole family would feel better knowing what is really happening.

By lonelygod — On Jul 27, 2011

My mother has been a heavy smoker her whole life but has recently noticed an increase in the brown phlegm she is producing and is worried that something may be going wrong with her lungs. We have tried to get her to quit smoking for years but to no avail.

Do you think that an increase in phlegm is a natural part of being a long-term smoker, or that there may be something more dangerous happening?

We are really worried she might have given herself lung cancer with all the puffing away she's been doing over the years. It is upsetting to think of how easily this all could have been avoided.

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