Linda Geddes, writing in The Guardian »

“Whenever we’re exposed to sounds and noise, the inner ear is translating that into nerve signals that are then interpreted by the brain,” he said. “It is an active process, which generates metabolites, some of which have been shown to be harmful to the inner ear. You probably want to have a period where the auditory system can wind down, regenerate and prepare for the next wake period.”

Colin Espie, a professor of sleep medicine at the University of Oxford, agrees the research quality of studies on continuous noise and sleep is poor. “Even the idea is a very limited one conceptually,” he said. “The main concern to overcome in poor sleep is the busy or racing mind. People can’t switch off mentally. White noise is just like any other monotonous stimulation, which has been tried many times in many ways over decades, and the evidence [for it working] is poor.”