Cure4CF Update

Spit Happens. From Phlegm to Facts: Understanding Wet Coughs  

 Professor Jodie Simpson, Head of Research, Cure4CF

Let’s talk about something we don’t often discuss openly—sputum. You might know it better as phlegm or mucus, and if you’ve ever had a wet or chesty cough, chances are you’ve coughed some up. That “rattly” sound in your chest? That’s a productive cough—your body’s way of clearing gunk from your lungs and lower airways.

Before I joined Cure4CF, I actually spent a lot of time working with sputum in the lab. (Yes, that was my job!) I even used to count cells in it to better understand inflammation in the airways. Trust me—there’s a lot more going on in that mucus than you’d think.

So, why does sputum matter?

Believe it or not, the colour of the sputum you cough up can give you (and your doctor) valuable clues about what’s going on in your lungs:

  • White or clear: This is typically normal, although it can become thicker during a cold or mild illness.
  • Yellow: This can suggest the start of an infection—your immune system is gearing up.
  • Green: Often a sign of a bacterial or viral infection. It usually means your immune system is in full swing, with lots of infection-fighting neutrophils.
  • Brown: This could be due to inhaling something (like smoke or dust), or it might be more common in heavy smokers.
  • Pink or Red: This indicates blood—always something to get checked out.

Dr Bernadette Prentice, a paediatric respiratory specialist and member of our Cure4CF Research Committee, sums it up simply:

“A wet cough that lasts more than four weeks is not normal—get it checked out.”

Why four weeks matter

At the recent World Bronchiectasis Conference in Brisbane, Dr Prentice highlighted just how tricky it can be to properly diagnose and manage a wet cough in kids. Often, a persistent wet cough is brushed off or goes unnoticed—especially if the child doesn’t look particularly unwell.

But here’s the thing: a chronic wet cough can be the only symptom of something much more serious. One common cause is Protracted Bacterial Bronchitis (PBB), an infection-driven condition that, if left untreated, can lead to lasting lung damage.

Even if your child isn’t coughing up visible phlegm, the sound of their cough can be a clue. Some kids (and adults) tend to swallow sputum instead of spitting it out, making it harder to spot.

Why early action is so important

If PBB isn’t treated, it can progress to Chronic Suppurative Lung Disease (CSLD)—a kind of middle stage where symptoms are getting worse, but there’s not yet visible structural damage to the lungs. Eventually, this can develop into bronchiectasis, a serious and irreversible condition where the airways become permanently widened and scarred.

Dr Prentice’s message is clear:

Don’t wait for a CT scan to show damage. If a wet cough is hanging around, treat it early and prevent things from getting worse.

The bottom line? 

Whether it’s your child or yourself, a persistent wet cough is worth paying attention to. If it lasts more than four weeks, don’t shrug it off— see a doctor. It might just be a lingering cold—or it might be something more. Either way, early treatment can make all the difference.

Stay tuned as we continue to bring these global insights home and translate them into real impact for Australians living with cystic fibrosis.