Eighteen years ago, Duncan Boak was on a night out with friends when he tripped and fell backwards down a flight of stairs, crunching his head against a concrete floor. When he was discharged from hospital and ate his first meal, it tasted of nothing. It was then that he realised he could not smell.

On visiting his GP, Boak was “met with a shrug” and told that there was nothing that could be done about it. Several years later, he came across a book which recounted the story of a woman with a similar experience to his own. It was thus that he learnt about the work of German scientist Professor Thomas Hummel – a smell and taste loss expert based at TU Dresden – and was inspired to get in touch with him. Boak spoke with Hummel and other specialists about the subject, became a lay expert, and founded the charity Fifth Sense in 2012.

‘Fifth sense’ refers not to taste (gustation) but to smell (olfaction): often placed at the bottom of the pile when it comes...