The fear of the dark is a common fear among children and to a varying degree is observed for adults. Fear of the dark is usually not fear of the darkness itself, but fear of possible or imagined dangers concealed by the 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 nyctophobia (from Greek νυξ, "night" and φοβια, phobia), scotophobia, from σκότος - "darkness", or lygophobia, from λυγή - "twilight" and achluophobia.
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]