People who smoke are more likely than non-smokers to develop pneumonia, if they catch coronavirus.
A Welsh respiratory expert said smokers are more vulnerable to the effects of the virus because their lungs are already weakened.
Ash Wales are urging people to quit smoking now "more than ever".
17% of the adult population in Wales smoke with deprived areas having the highest numbers.
Keir Lewis, Professor of Respiratory Medicine at Swansea University, said smokers have damaged the cells protecting their nose and airways. This means they are more likely to develop lung problems as a result of contracting Covid-19.
Many smokers will also have existing lung conditions which puts them at an even greater risk.
A study published in the New England Journal of Medicine found that smokers were around one-and-a-half times more likely to progress to the severe stage of coronavirus than those who do not smoke.
It looks like if you have a respiratory condition then you are more likely to develop viral pneumonia from Covid-19.
According to Professor Lewis, lung defences can start to heal within days so giving up smoking now could significantly improve smokers' ability to defend and recover from the infection.
He added that by quitting, those who contract the virus are less likely to pass on the condition to others.
If they cough less after stopping smoking with their asthma or COPD they are less likely to pass it on to those around them. Now is a good trigger to stop smoking.
Suzanne Cass, CEO of ASH Wales, said: "Smoking is not a lifestyle choice, it is an addiction that leads to devastating health consequences, which is why we would always advise smokers to quit.
"However, in light of concerns about the spread of Covid-19 we would urge smokers more than ever to consider giving up a habit that seriously affects the body's natural defences."
Smoking is the leading cause of premature death and ill health in Wales.
On Tuesday, it was confirmed that a second person in Wales had died from coronavirus.
The first patient was a 68-year-old in Wrexham whilst the second was 96 years old and was being treated at Morriston Hospital in Swansea.
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