The ads are everywhere – as are the inflated claims: special shampoos and treatments, sometimes costing thousands of dollars, will make hair grow. But many dermatologists who specialise in hair loss say most of these products do not work.

“There is an endless array of useless hair-growth remedies,” often at “significant cost,” said Dr Brett King, a dermatologist at Yale School of Medicine. Yet, he added, “because people are desperate, such hair growth remedies continue to abound.”