Phlegm, mucus and asthma

What does the colour of your phlegm mean? And is coughing up mucus a bad sign if you have asthma? We answer your questions.

Does coughing up lots of phlegm/mucus mean you have asthma?

Some people who have asthma do find they cough up phlegm. But being very ‘phlegmy’ doesn’t mean you have asthma. To be diagnosed with asthma, you’d also need to show other symptoms.

If you’re worried you have asthma, start by reading our symptoms page. Then the next step is to talk to your doctor.

By the way, if you’re wondering what the difference between phlegm and mucus is, well, there isn’t really one. Mucus is a jelly-like liquid found in the lungs, airways, digestive system and other parts of the body. It looks gross, but it protects you from infection. And phlegm (or sputum as your doctor might call it) is the specific name for mucus that you cough up from your lungs.  

Is phlegm a sign your asthma’s getting worse?

Coughing up more phlegm than usual could be a sign your airways are inflamed, meaning they get narrower and cause other asthma symptoms like coughing, wheezing, chest tightness and breathlessness. Imagine the air you breathe in trying to get through narrow, mucus-filled tunnels.

If you’re struggling for breath, your reliever inhaler will help open up your airways in the short-term. If you’re using your reliever inhaler more than three times a week you need to see your doctor. 

Taking your daily preventer inhaler as prescribed should help stop these symptoms, because they reduce the inflammation in your airways over time.  

What the colour and thickness of your phlegm means

The colour of your phlegm can change when you’re ill.

If you feel unwell and you’re worried because your phlegm’s a different colour or thickness than usual, visit your doctor. They might look at or test a sample of your phlegm to find out more.  

Phlegm is different from person to person and condition to condition, so isn’t a 100% accurate guide to what’s going on in your lungs. But here are some pointers:

White phlegm

Shows: producing a bit of white or clear phlegm every now and then is completely normal – you don’t need to worry about it.

Effect on asthma: a small amount of white phlegm shouldn’t affect your asthma. But lots could be a sign your airways are inflamed, and your asthma symptoms might be getting worse.

Action: you need to calm the inflammation in your airways. Your preventer inhaler is the number one way to do this, as long as you’re taking it as prescribed by your doctor or nurse.

If you’ve been taking your preventer but nothing’s improving see your doctor. They might need to tweak your medication or help you manage triggers or allergies like hay fever.

Solid bits of phlegm: some people find they also cough up little pearls of white in their phlegm. These are from lower down in your airways where phlegm has got a bit stuck. They’re not usually anything to worry about – you should have less if your asthma is well managed.

Yellow or green phlegm

Shows: this might be a sign of an infection. It could be a cold, the flu or a chest infection. Green phlegm’s more likely to be a sign of a bacterial infection than yellow phlegm (though you can’t tell just by looking).

Effect on asthma: infections often trigger asthma symptoms, meaning you might have a cough, wheeze, chest tightness, wheeze and feel breathless.

Action: read our pages on colds and flu, or on chest infections to find out more about the symptoms and what you can do to get better.

Take your preventer inhaler as prescribed to build up protection against colds and the flu. The preventer dampens down the inflammation in your airways which makes your asthma symptoms worse. 

Streaked red phlegm

Shows: you’ve been coughing a lot, maybe because of a chest infection or your asthma. Long coughing fits put a lot of pressure on your lungs. This makes your blood vessels leak a bit, which might be why your phlegm is streaked with blood.

Effect on asthma: chest infections often trigger asthma symptoms. If you don’t have a chest infection but you’re coughing a lot, this could be a symptom of your asthma.

Action: see your doctor. They can help reduce your asthma symptoms so you stop coughing as much, or treat your chest infection.  

Important: If you’re coughing up blood (not just streaked phlegm) call your doctors and ask for an urgent appointment.

Brown or black phlegm

Shows: you might get brown-tinged phlegm if you smoke or if you have COPD as well as asthma..

Effect on asthma: the chemicals in cigarettes trigger asthma symptoms. Plus, smoking can stop your preventer inhaler working – so your airways aren’t protected from other triggers either. It can also make your asthma worse in the long-term by changing your airways.

Action: just three days after you’ve stopped smoking, your airways will get less inflamed. Read our advice on quitting.

Treatment for producing too much phlegm

If you’re taking your preventer and you still feel like there’s lots of mucus on your chest, your doctor can help. They might suggest you see a physiotherapist who can teach you exercises called the ‘Active Cycle of Breathing Techniques (PDF, 448 KB)’ to help clear the mucus from your chest. 

There are also medicines that can help mucus break down, so you can cough it up more easily. Speak to your doctor about these if you’re not able to cough up the mucus and feel really ‘clogged up’.

The flu vaccine is free for people with asthma - see our vaccines advice for more.