Fear of the dark

Fear of the dark is a common fear or phobia among children and, to a varying degree, adults. A fear of the dark does not always concern darkness itself; it can also be a fear of possible or imagined dangers concealed by darkness. When waking or sleeping, these fears may intertwine with sighting sleep paralysis demons. Some degree of fear of the dark is natural, especially as a phase of child development. Most observers report that fear of the dark rarely appears before the age of two years. When fear of the dark reaches a degree that is severe enough to be considered pathological, it is sometimes called scotophobia (from σκότος – "darkness"), or lygophobia (from λυγή – "twilight").

Some researchers, beginning with Sigmund Freud, consider the fear of the dark to be a manifestation of separation anxiety disorder.

An alternate theory was posited in the 1960s, when scientists conducted experiments in a search for molecules responsible for memory. In one experiment, rats, normally nocturnal animals, were conditioned to fear the dark and a substance called "scotophobin" was supposedly extracted from the rats' brains; this substance was claimed to be responsible for remembering this fear. These findings were subsequently debunked.