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 the darkness itself, but fear of possible or imagined dangers concealed by the darkness.Some degree of fear of the dark is natural, especially as a phase of child development. Most observers report that fear of the dark seldom appears before the age of 2 years. 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”).
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.