‘I wish that by plucking a single hair you would get more to grow back,” says Desmond Tobin, professor of dermatological science at University College Dublin. “It would be a great solution for people who are thinning and unhappy about it.”

Unfortunately, it’s a myth. Our scalp is covered in follicles – essentially tiny hair factories – and each one produces just a single hair shaft. Plucking a hair won’t cause multiple hairs to grow from the same follicle.

In fact, repeatedly pulling hairs out can have the opposite effect. Over time, the damage may mean the hair never grows back at all. Tobin points to the ultra-thin eyebrow trend of the 1990s and early 2000s, when many people overplucked and found their follicles simply stopped producing hair. “They weren’t getting two for every one,” he says. “They were actually getting none.”

Damage is the key issue. “You may fracture the hair as you pluck it, or pull it out by the root,” Tobin explains. “Sometimes when you see tiny blood droplets on the skin, you know you’ve removed the entire follicle and it will not recover.”

Is there anything you can do to discourage grey hairs from appearing? It is largely genetic, says Tobin. Looking at close relatives can give you a sense of what to expect. That said, chronic stress, poor sleep and nutritional deficiencies may accelerate aspects of biological ageing, including changes in the hair.

Still, grey hair isn’t necessarily a negative development. It often grows just as well as – and sometimes better than – pigmented hair. Men with salt-and-pepper beards, for example, frequently notice that white hairs grow longer between shaves. “There seems to be a preferential growth-rate advantage to white and grey hair,” says Tobin.