Clear or white phlegm is generally normal, while green, yellow, red, brown, black, or pink frothy phlegm can signal something that needs attention. The color of your phlegm changes based on what your immune system is doing, what you’ve been exposed to, and whether infection or inflammation is present. Not every color change means you’re seriously ill, but some colors are genuine red flags.
Why Phlegm Changes Color
Your body produces mucus all the time to keep your airways moist and trap particles like dust and germs. When you’re healthy, that mucus is thin and clear. Color shifts happen when your immune system ramps up. White blood cells called neutrophils rush to your airways to fight off invaders, and those cells contain an enzyme with a green pigment. The more neutrophils that accumulate, the more green your phlegm becomes. A smaller immune response produces yellow; a larger one turns things darker green. This is why color deepens as an infection progresses.
Clear and White Phlegm
Clear phlegm is the baseline. If you’re coughing it up in larger amounts than usual, your body is likely flushing out allergens like pollen, dust, or pet dander. It can also increase with a cold in its earliest stages.
White phlegm is a step up from clear but still relatively common. It’s associated with viral bronchitis, acid reflux (GERD), COPD, and congestive heart failure. On its own, white phlegm rarely means you need antibiotics. If it persists for more than a few weeks or comes with shortness of breath, it’s worth investigating further.
Yellow Phlegm
Yellow phlegm means your immune system is actively working. In otherwise healthy people, it most often points to viral bronchitis, not a bacterial infection. The yellow tint comes from a moderate concentration of those neutrophil enzymes. A pooled analysis published in the European Respiratory Journal found that about 46% of yellow sputum samples contained bacteria, compared to only 18% of clear samples. That’s a meaningful increase, but it also means more than half of yellow sputum samples had no bacterial cause at all.
The takeaway: yellow phlegm during a cold or upper respiratory infection is expected and doesn’t automatically mean you need antibiotics. It typically clears within one to three weeks.
Green Phlegm
Green is where people start to worry, and for good reason. Green phlegm indicates a high concentration of immune cells fighting in your airways. About 59% of green sputum samples yield bacteria, making it the strongest color predictor of a bacterial presence. In people with COPD, green sputum is considered a reliable marker of bacterial exacerbation where antibiotics are most likely to help.
That said, green phlegm can also appear during severe viral infections. The color alone doesn’t confirm you need treatment. What matters more is the combination of symptoms: how long it’s lasted, whether you have a fever, and whether you’re getting worse instead of better. Green phlegm persisting beyond two to three weeks, or accompanied by high fever and worsening breathlessness, points more strongly toward a bacterial infection like chronic bronchitis, a lung abscess, or cystic fibrosis flare-up.
Red or Bloody Phlegm
Any amount of blood in your phlegm deserves attention. Small streaks of red mixed into mucus can happen from something as minor as forceful coughing that irritates your airway lining, or from acute bronchitis. These causes, while uncomfortable, are common and usually resolve on their own.
Larger amounts of blood, or blood that keeps appearing over several days, raise the stakes considerably. Possible causes include pneumonia, tuberculosis, blood clots in the lungs (pulmonary embolism), bronchiectasis, and lung cancer. Red flags that make bloody phlegm more urgent include unexplained weight loss, fatigue, back pain, a long history of heavy smoking, or difficulty breathing at rest. Coughing up a large volume of blood is a medical emergency regardless of other symptoms.
Rust-Colored Phlegm
Rust or reddish-brown phlegm sits between red and brown on the spectrum and often indicates old blood that’s been in the lungs for a while. It’s classically associated with a type of bacterial pneumonia caused by pneumococcus, but can also show up with pulmonary embolism, tuberculosis, or lung cancer. If your phlegm turns rust-colored during what seemed like a routine chest infection, it’s a sign the infection may be more serious than a typical cold or bronchitis.
Brown and Black Phlegm
Dark brown phlegm often represents the deepest end of the infection color spectrum. Research on COPD patients found that as sputum color deepens from yellow to brownish, the likelihood of more aggressive bacteria increases. Brown phlegm can also come from inhaling heavy amounts of dust, dirt, or tobacco smoke over time.
Black phlegm, known medically as melanoptysis, is rare and almost always tied to significant environmental exposure or serious lung disease. The most common causes are pneumoconiosis (lung disease from inhaling coal dust, silica, or similar particles) and chronic smoke inhalation, which is why it appears in firefighters. Certain fungal infections can also produce black phlegm. Some species of fungi naturally produce dark pigments, and when they infect lung tissue, they can discolor sputum. If your phlegm is black and you haven’t been exposed to heavy smoke or coal dust, a fungal infection or another underlying condition needs to be ruled out.
Pink Frothy Phlegm
This is one of the most urgent colors on the list. Pink or white frothy sputum is a hallmark of pulmonary edema, a condition where fluid fills the air sacs in your lungs. It can happen with congestive heart failure or at very high altitudes. The frothy texture is key: it looks like soap bubbles rather than thick mucus, sometimes tinged pink with small amounts of blood. This combination of pink color and foamy consistency is a distinct warning sign that your lungs are filling with fluid, and it requires emergency medical care.
How Long Colored Phlegm Lasts
After a typical respiratory infection, colored mucus and coughing can persist for up to three weeks, even after you feel better overall. Your airways stay inflamed for a while after the infection clears, and the lingering phlegm doesn’t necessarily mean you’re still contagious or that the infection has worsened. The color should gradually lighten from green or yellow back toward white or clear over that period. If it’s getting darker instead of lighter, or if new symptoms like fever or chest pain develop after an initial improvement, that pattern suggests a secondary bacterial infection may have taken hold.
Colors That Need Prompt Attention
- Red or bloody: Any significant or recurring blood in phlegm, especially with weight loss, smoking history, or breathlessness
- Rust-colored: Suggests pneumonia or other serious lung conditions
- Pink and frothy: Points to fluid in the lungs, a medical emergency
- Black: Indicates heavy environmental exposure or rare infections
- Green or yellow lasting more than three weeks: May indicate a bacterial infection that isn’t resolving on its own
Color is a useful clue, but it’s one piece of the puzzle. How you feel overall, how long symptoms have lasted, and whether you’re improving or declining matter just as much as the shade of what you’re coughing up.