‘That’s not true,” says Desmond Tobin, professor of dermatological science at University College Dublin. Hair grows from follicles – tiny structures in the scalp sitting 2-4mm beneath the skin. Inside each follicle, the hair fibre is formed long before it becomes visible at the surface of the scalp. By the time it emerges, the hair that you’re cutting is dead, hardened tissue.
“Cutting what’s above the surface has no effect on what’s happening in the follicle below,” says Tobin.
Hair growth happens at a rate of around 1cm a month during a growth phase that lasts several years, before the hair is shed and the cycle begins again. That rate is determined by genetics and can’t be sped up with scissors.
What does change is how long hair appears to grow. Heat styling and aggressive chemical treatments can damage the outer shaft, making it brittle and prone to splitting. When hair breaks faster than it grows, it never seems to get any longer.
So where does the myth come from? Think of trimming an unruly hedge, Tobin says. “When you give it a good clip into shape, it can give the impression of being denser. You haven’t changed what’s happening in its deeper branches – you’ve just tightened up the overall appearance.”
Hair behaves in much the same way. Individual strands taper as they get further from the scalp, so cutting them shorter makes them feel thicker. Removing frayed, weathered ends can also make hair look fuller and healthier.
If you’re trying to grow your hair, Tobin says, the priority isn’t frequent trims but minimising damage. “The advice would be to maintain the hair fibre in a virgin state with the least aggressive chemical or thermal exposure.”
