Smoking causes lung damage© Getty

"Without treatment, the symptoms usually get progressively worse," the NHS says.

"There may also be periods when they get suddenly worse, known as a flare-up or exacerbation."

People who have persistent symptoms of COPD, particularly if over the age of 35, are strongly advised to "see a GP" if they smoke, or used to smoke.

Treatment is advised as soon as possible, before the lungs become "significantly damaged". 

 Vaping could lead to persistent coughing
Vaping could lead to persistent coughing© Getty

The NHS adds: "The likelihood of developing COPD increases the more you smoke and the longer you've smoked."

While the damage to the lungs caused by COPD is "permanent", treatment can help to slow down the progression of the disease.

Treatments can include inhalers and medications to help make breathing easier, and pulmonary rehabilitation.

People who have COPD are strongly advised to stop smoking - it's the "most important thing you can do".