The fear of the dark is a common fear or phobia among children and, to a varying degree, of adults. Fear of the dark is usually not fear of darkness itself, but fear of possible or imagined dangers concealed by darkness.^[1] Some degree of fear of the dark is natural, especially as a phase of child development.^[2] Most observers report that fear of the dark seldom appears before the age of 2 years.^[3] When fear of the dark reaches a degree that is severe enough to be considered pathological, it is sometimes called achluophobia, nyctophobia (from Greek νυξ, “night”), scotophobia (from σκότος – “darkness”), or lygophobia (from λυγή – “twilight”).

Some researchers, beginning with Sigmund Freud, consider the fear of the dark as a manifestation of separation anxiety disorder.^[4]

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. Subsequently, these findings were debunked.^[5]