Freud believed that as children age, they progress through five stages, in four of which they derive sexual pleasure from a specific part of their bodies. According to Freud, at each stage, a battle between the person's biological needs and society's expectations takes place. Freud hypothesized that the amount of sexual gratification parents allow their children at these different stages has an effect on them as adults. While Freud's psychosexual theory has been criticized for its limitations, datedness and what some consider its overemphasis on the role of sexuality in how people mature, it retains an important position in the study of human development to this day.
From birth until a child is 1 year old, Freud theorized an individual's psychic and sexual energy is concentrated on the mouth, from which he receives all his initial pleasure through breastfeeding. An adult whose psychosexual maturation becomes "fixated" in the first stage of Freud's theory of development wants to return to an anxiety-free point in his life associated with sucking at his mother's breast. A person with an oral fixation may find pleasure in smoking, biting fingernails, or overeating or drinking. A person "stuck" at the first stage of development may be characterized as gullible and dependent upon others, or she may become aggressive and pessimistic from fighting her oral urges.
Toddlers from ages 2 to 3 have reached Freud's second stage of psychosexual development. Freud believed that children at this age connect their developing understanding of societal rules and regulations to the pleasure they find in controlling their bowel movements. He theorized that if a person is frustrated while being toilet trained, she may become "fixated" at this anal stage and grow into an adult who is stingy, stubborn, compulsively messy or compulsively clean.
Freud's third stage of development is the phallic stage; it dominates from about age 3 to 6. According to Freud, during this time a child finds pleasure in the genitals. He believed boys develop unconscious sexual desires for their mother and feel they must compete with their father for their mother's affection. This theory is known as the Oedipus complex. Freud theorized that out of fear, boys ultimately choose to identify with their father instead of fight him and learn to repress sexual feelings for their mother. People who become "stuck" with a genital fixation left over from this period may either overindulge in or avoid sex altogether, or may become confused about their sexual identity.
Freud's full psychosexual theory includes two more stages: the latent stage, in which a child's sexual development goes into a dormant period as he focuses on school from about age 6 until puberty, and the genital stage, at which children grow into their sexual maturity and refocus their source of sexual pleasure in the genitals in preparation for adulthood.