Castration anxiety is the fear of emasculation in both the literal and metaphorical sense. Castration anxiety is an overwhelming fear of damage to, or loss of, the penis—a derivative of Sigmund Freud's theory of the castration complex, one of his earliest psychoanalytic theories. Although Freud regarded castration anxiety as a universal human experience, few empirical studies have been conducted on the topic. It has been theorized that castration anxiety begins between the ages of 3 and 5, otherwise known as the phallic stage of development according to Freud. In Freud's theory it is the child's perception of anatomical difference (the possession of a penis) that induces castration anxiety as a result of an assumed paternal threat made in response to their sexual activities. Although typically associated with males, castration anxiety is theorized to be experienced in differing ways for both the male and female sexes.