4. Where you live

“Air pollution can also damage hair colour in much the same way as cigarette smoke does,” Proudman explains. “When inhaled and absorbed into the bloodstream, toxins such as diesel fumes can trigger oxidative stress – damaging healthy cells in the scalp, reducing their ability to produce the melanin needed to retain colour.”

While grey hair is by no means a bad thing, there are ways to slow down greying due to air pollution, Proudman adds. “If you live in a built-up area, washing your hair regularly – at least every other day – can get rid of polluted particles that could penetrate the hair and damage melanocyte cells in the scalp. You could also consider using an antioxidant-rich conditioner, that can help protect against toxic deposits that might speed up the greying process.”

5. Sun exposure

“Too much sun exposure isn’t just bad for your skin – it can also drain the colour out of your hair,” Proudman says. “Excess UV light triggers the same oxidative stress that smoking does, damaging melanin-producing cells in the scalp and speeding up the greying process. Studies show that UV rays also disrupt levels of keratin, a protein in hair that strengthens and protects it.”

6. Heat exposure

In a similar way to the sun, too much heat can wreak havoc on the cells on your head. “Most household hairdryers heat to between 20° C and 60° C. At the top end of that range, it’s enough to ‘bake’ not only the hair but the delicate melanin-releasing cells in the skin and hair follicles, turning off the supply of pigment to each strand of hair.”

“Can stress actually turn your hair grey?” A trichologist explains