It used to be thought that the lungs couldn’t regenerate,” says Dr Charlotte Dean, head of the lung development and disease group at Imperial College London. “But we know now that’s not the case. Broadly speaking, they can repair when you quit smoking.”

Smoking is in effect damaging your lungs, Dean says, and the lungs have a substantial capacity to heal themselves. They have evolved to cope with pollution or getting infected by bacteria or viruses. “Because they’re so vital – you can’t survive without your lungs – they needed to have this capacity,” she says.

Dean says this shouldn’t be used as an excuse to smoke, though; smoking and vaping expose your lungs to more toxic particles than they can cope with. Importantly, everyone is different and some people’s lungs will not be able to regenerate as well as others and so will be much more susceptible to permanent tissue damage from smoking.

“While it’s broadly true that if you stop smoking you can revert to having much better lung health, it doesn’t mean you’re completely out of the woods. You may well have triggered mutations or genetic changes or tissue damage, and those things can affect your overall lung health, meaning that the decline as you age will come quicker or could lead to cancer.”

She would encourage smokers to quit as early as possible as – similarly to how your bones don’t mend as well as you age – your lung tissue gets less effective at repairing itself as you get older. A healthy lifestyle can help. “Exercise is really important,” says Dean. “Just like how when you exercise you keep your muscles healthy, in a way the lungs are the same. You build up the capacity for gas exchange to happen more effectively, to provide oxygen around the body.”