Green, Yellow & Brown Phlegm: Learn Everything You Need

Introduction

Phlegm isn’t something most people want to think about, but when it changes colour, it’s hard to ignore. That thick mucus in your throat or chest is more than just an annoyance — it’s a sign of what’s happening inside your body. 

What is phlegm, and why does it change colour? 

Phlegm is a type of mucus produced by the respiratory system. It helps trap dust, allergens and germs before they reach the lungs. Most of the time, it’s clear and barely noticeable. But when your body is fighting off an infection or reacting to irritants, it thickens and takes on a colour.

The colour shift happens due to white blood cells, bacteria and other immune responses in your system. If you’ve been coughing up green phlegm, you might be wondering whether it’s a sign of a chest infection or something else. 

Below, we break down what different phlegm colours mean and when it’s worth paying closer attention.

Green phlegm: a sign of a battle in progress

Green mucus is often linked to infections, but it doesn’t always mean you need antibiotics. The green colour comes from white blood cells that rush to fight off bacteria or viruses. As they break down, they release enzymes that give phlegm its greenish tint.

Common causes of coughing up green phlegm include:

• Viral infections – Colds and flu can cause green mucus, even without a bacterial infection.

• Bacterial infections – Sinus infections, bronchitis and pneumonia sometimes lead to green mucus, especially if symptoms last longer than 10 days.

• Post-nasal drip – Allergies or sinus congestion can cause thick, green mucus to collect in the throat.

If coughing up green phlegm doesn’t stop for more than two weeks, comes with a high fever or is accompanied by shortness of breath, it’s time to check in with a doctor.

Yellow phlegm: your immune system at work

Yellow phlegm is a sign that your immune system is responding to an infection. It’s not as severe as coughing up green phlegm, but it still indicates that your body is in defence mode.

Common causes of yellow phlegm include:

• Common cold – A mild cold can cause yellow mucus as the body clears out the virus.

• Sinus infections – If a sinus infection lingers, yellow phlegm may be a sign of inflammation and congestion.

• Respiratory infections – Mild bronchitis or other viral infections may cause yellowish mucus.

If yellow phlegm turns darker or comes with worsening symptoms, it could be progressing into something more serious, like a bacterial infection.

Brown phlegm: what’s getting into your lungs?

Brown mucus is usually linked to inhaling particles from the environment. Smokers and those exposed to dust, pollution or occupational hazards often notice brown or rust-coloured phlegm. It can also indicate old blood mixing into mucus.

Common causes of brown phlegm include:

• Smoking – Tar and toxins from cigarettes can stain mucus brown over time.

• Inhaled irritants – Dust, dirt and air pollution can mix with mucus and create a brownish tinge.

• Chronic lung conditions – Conditions like bronchitis or COPD may produce brown phlegm.

• Old blood in mucus – If you’ve had a bad cough, small blood vessels may have broken, leading to rust-coloured mucus.

Brown phlegm isn’t always a cause for concern, but if it appears suddenly, persists or comes with symptoms like chest pain or difficulty breathing, it should be checked out.

Chest infections and when to see a doctor

Coughing up green phlegm for more than two weeks can sometimes point to a chest infection, especially if it’s paired with fatigue, fever or difficulty breathing. While some infections clear up on their own, others may require treatment.

In cases of bacterial infections, doctors may prescribe antibiotics for chest infections if symptoms are severe or prolonged. However, antibiotics won’t help with viral infections, so it’s important to get the right diagnosis.

See a doctor if:

• Phlegm lasts more than two weeks

• You have chest pain, fever or shortness of breath

• Your mucus contains blood

• Symptoms worsen instead of improving

Ignoring persistent symptoms can lead to complications, especially for people with asthma, COPD or weakened immune systems.

Taking care of your lungs to avoid phlegm buildup

Phlegm buildup is a signal to take extra care of your respiratory system. You can clear it out by: 

• Hydrating to thin mucus and make it easier to expel

• Taking a hot shower or using a humidifier to loosen mucus

• Avoiding smoking and pollution to reduce lung irritation

• Getting plenty of rest to help your body fight off infection

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