[So] says Rachel Herz, a professor of psychiatry at Brown University and author of The Scent of Desire. Her research and experiments indicate people do not respond to odours while they are in the dreaming phase of sleep (REM) or deep sleep. “You cannot smell while you are asleep,” she says. “You don’t smell the coffee and wake up; rather you wake up and then smell the coffee.” But, she says, if we very briefly wake up and perceive the scent of coffee, it will wake us further if we are interested in it. Any odours that are experienced in dreams, like [Smell Festival director Francesca] Faruolo’s, are “created by the brain not from outside”.
That is one theory. Prof Thomas Hummel of the University of Dresden’s Smell and Taste Clinic has another. His research corroborates Herz’s conclusion that smells do not rouse us from sleep, but olfactory stimuli do influence our dreams, he suggests. In one experiment, in which volunteers were stimulated with hydrogen sulphide (the rotten-egg stink-bomb smell) and phenyl ethyl alcohol (which resembles the smell of roses), participants reported having more positive dreams with the sweet-smelling stimulus and more negative dreams with the foul-smelling one.