Phlegm, mucus and asthma

Find out why coughing up more phlegm than usual can be a sign that your airways are inflamed and how to tell one kind of phlegm from another by the colour

What is phlegm?

Phlegm is the specific name for mucus that you cough up from your lungs. Your doctor might call it ‘sputum’. And mucus is a jelly-like liquid found all over the body that protects you from infection.

Coughing up lots of phlegm doesn't mean you have asthma, although some people with asthma do find they cough up lots of phlegm.  

What does phlegm mean?

Coughing up more phlegm than usual could be a sign that your airways are inflamed. This means your airways get narrower and this can cause other asthma symptoms, like:

  • coughing
  • wheezing
  • breathlessness.

If you have more asthma symptoms than usual, your reliever inhaler will help open up your airways. But remember, 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 reduce the inflammation that’s causing your asthma symptoms. Find out more about how preventer inhalers help asthma.

What does your phlegm mean?

Asthma + Lung UK nurse Claire explains how phlegm relates to asthma and what to look out for in terms of colour, thickness or amount. 

Hi, I’m Claire, a respiratory nurse specialist at Asthma + Lung UK. I’m going to talk to you about what your phlegm means.

Although it’s not nice to see, phlegm and mucus are part of your body’s defence against infection. It’s part of the protective coating of the airways in the lung.

Coughing up a little bit of phlegm occasionally is totally normal, but if your phlegm changes in colour, thickness, or amount, it could be a sign that you're unwell.

If you find you've been coughing up more phlegm than usual, this could be a sign of inflammation or a flare-up of your lung condition. Make sure you keep taking all your medicines as prescribed.

If you’re still coughing up more phlegm than usual, book an appointment with your GP, doctor, or nurse.

If you have bronchiectasis or COPD, you may need to send a phlegm sample to your healthcare professional to test for an infection.

If you are coughing up yellow or green phlegm, this could be a sign of a chest infection, cold, or flu. It’s really important to keep taking your medicines as usual to control your symptoms. However, if you’re concerned, speak to your GP, doctor, or nurse.

If you have COPD or bronchiectasis, you might have a rescue pack of antibiotics and steroids to take in case of a chest infection. You should be given a written plan with instructions on how and when to take them. Speak to your healthcare professional if you’re not sure.

Coughing up blood can have lots of different causes. Some of these are not serious, but some can be very serious, like clots on the lung or lung cancer. Always let your doctor know if you cough up blood, so they can help to find out the cause.

If you’re coughing up more than just a few streaks of blood, then you should call 999.

Brown phlegm can be caused by a chest infection but black or brown phlegm usually happens in people who smoke or people who have been exposed to dust or dirt, such as coal workers. It can also happen in people with COPD. Speak to your healthcare professional if your phlegm is black or brown.

If you smoke, you should try to quit. Quitting will mean you can manage your lung condition better and is one of the best things you can do for your lung health.

If you have questions about phlegm and your lung condition, speak to your doctor, nurse, or pharmacist. You can also call our helpline.

What does the colour mean?

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, speak to your doctor. They might look at or test a sample of your phlegm to find out more.  

Everyone’s phlegm looks different and it isn’t a completely accurate guide to what’s going on in your body. 

White phlegm

A bit of white or clear phlegm every now and then is completely normal.

However, if you’re producing lots of white or clear phlegm, it could be a sign that your airways are inflamed and your asthma symptoms might be getting worse.

It’s worth remembering that your airways include the nose and sinuses, as well as your throat. It may be that the mucus you’re coughing up has moved from your nose or sinuses to the back of your throat or chest. If you get symptoms in your nose and sinuses – such as mucus, sneezing or an itchy or blocked nose – speak to your GP or pharmacist about how you can treat this. Treating your nose and sinuses can improve your asthma symptoms too.

Your preventer inhaler is the number one way to deal with 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 or asthma nurse. They might need to change your medication or help you manage your triggers or allergies, like hay fever. 

Yellow or green phlegm

This might be a sign of an infection, like a cold, the flu or a chest infection.

Infections often make asthma symptoms worse. This is why it’s really important to keep taking your preventer inhaler every day, as this helps to control your asthma.

Find out how to reduce your risk of catching a cold or the flu if you have asthma. 

Streaked red phlegm

If you cough up blood, call your GP surgery as soon as possible, even if it's just a tiny bit of blood.

Coughing up blood can be alarming, but it doesn’t necessarily mean there’s a serious problem. If you cough up blood, it is usually because you have been coughing a lot or you have a chest infection.

Read about the common causes of coughing up blood, as well as some less common ones. 

Brown or black phlegm

There are a few reasons you might get brown or black phlegm and one of these is smoking.

It’s very important that you quit smoking, as it can make your asthma worse in the long term and trigger asthma symptoms in the short term.

Just three days after you’ve stopped smoking, your breathing will become easier and you'll have more energy. Get help to quit smoking.

Coughing up brown phlegm can also be a symptom of pneumonia. If you’re coughing up brown or black phlegm, it's really important that you book an appointment with your GP. 

Did you find this information useful?

We use your comments to improve our information. We cannot reply to comments left on this form. If you have health concerns or need clinical advice, call our helpline on 0300 222 5800 between 9am and 5pm on a weekday or email them.

Page last reviewed:
Next review due: