Harry Potter author JK Rowling says a breathing technique has helped her coronavirus-like respiratory symptoms, a claim that has been widely reported and shared on social media.

Her tweet includes a video from a UK hospital doctor describing the technique, a type of controlled coughing. This involves taking six deep breaths and on the last one covering your mouth and coughing.

The internet is full of home grown cures for the coronavirus. And when doctors propose them, they appear credible.

While special breathing techniques have their place in hospital, under the supervision of a respiratory physiotherapist or respiratory doctor, and for certain medical conditions, using them at home to manage coronavirus symptoms could be dangerous.

The technique in the video could help spread the coronavirus to people close by.

By coughing, you could directly infect people with droplets, or these droplets on someone’s hands can be transferred to a surface others can touch.

So JK Rowling’s well-meaning advice could inadvertently help spread the virus to your family, or to the person next to you on the bus.

Controlled coughing helps with cystic fibrosis

The cells in our lungs produce a sticky mucus as part of our body’s defence system. And when we have a viral lung infection, such as with the virus that causes COVID-19 or the influenza virus, we produce more of it.

The mucus traps the invading pathogen. Normally, this mucus is removed from the lungs by the movement of tiny hair-like projections in our airways. From there, we either swallow the mucus or cough it out as phlegm.

Read more: Health Check: why do I have a cough and what can I do about it?

However, sometimes we produce so much mucus it is difficult to breathe. The mucus can block our tiny airways, preventing us from obtaining oxygen from our lungs.

In other diseases, such as cystic fibrosis, controlled coughing can help remove the mucus and make it easier for people to breathe.

This technique may be done as part of chest physiotherapy, along with other lung clearance techniques, in a hospital. The technique is not dangerous, but the contents of what is coughed out can be.

Read more: Explainer: what is cystic fibrosis and how is it treated?

So can it help with the coronavirus?

So what’s the evidence controlled coughing could help people manage their coronavirus symptoms? Put simply, there are no clinical trials or good evidence.

One common COVID-19 symptom is a dry cough. So it’s difficult to imagine why controlled coughing would help when you’re coughing so much anyway.

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Is there any harm in trying?

There is a very real risk that unintentionally this technique would actually spread the virus.

When we cough we produce a lot of droplets of mucus from the lungs that are spread as a spray. My research has also shown breathing out forcefully is enough to propel viruses from the lungs this way.

Either way large sprays of viruses could infect other people.

In hospital, this risk is minimised by having specialised negative pressure rooms that remove the contaminated air. Patients wear masks to capture the sprays and clinical staff wear personal protective equipment, including masks and face shields. There are also strict infection control measures, such as limits on visitors and hand washing. Yet the risks of transmission remain high.

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But if you practise controlled coughing at home or on the bus, it’s easy to see how you could inadvertently spread the virus.

And of course, the technique doesn’t kill the virus or cure anyone.

So what are we to make of all this?

So why did JK Rowling endorse this technique? In essence, it’s because she believed it helped her, and thought it would help others.

However, her tweet says she hadn’t been tested for COVID-19, so it’s not certain she had the infection. And she may or may not have benefited from the technique. Perhaps her symptoms may have improved by themselves anyway. It’s hard to know.

My advice is to seek medical advice if you suspect you have the coronavirus rather than rely on testimonials, however well meaning.

Read more: Coronavirus: how long does it take to get sick? How infectious is it? Will you always have a fever? COVID-19 basics explained