Petra puts damaged hair under the microscope and finds out how to keep your crowning glory in top condition – and it will cost you. Can hair-care products strengthen, lengthen and even repair our hair? Is salon shampoo any better than supermarket? What happens when we don’t shampoo at all? Do hair repair products actually work? Are there cancer-causing chemicals in any of these products? And we comb through the evidence on balding and hair-loss products.