According to the late, great trichologist Philip Kingsley, it’s a myth that hair gets ‘used’ to the same shampoo. (He went so far as to say this was dreamed up by shampoo manufacturers to encourage you to switch brand – and ideally, buy theirs.) ‘The reason a change of shampoo can work wonders is because your hair may have changed,’ was his advice. ‘You may have had colour added, grown it longer or had it cut shorter, which all affect your hair’s needs.’ So the best time to assess whether you need to change products is if you’ve just ticked one of those boxes. Otherwise, feel free to stick with what you love.