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In Freudian psychoanalysis, the term oral stage denotes the first psychosexual development stage where in the mouth of the infant is his or her primary erogenous zone. Spanning the life period from birth to the age of 21 months, the oral stage is the first of the five Freudian psychosexual development stages: (i) the Oral, (ii) the Anal, (iii) the Phallic, (iv) the Latent, and (v) the Genital. Moreover, because it is the infant’s first human relationship — biological (nutritive) and psychological (emotional) — its duration depends upon the child-rearing mores of the mother’s society. Sociologically, the duration of infantile nursing is determined normatively, because the oral stage is especially important in societies that consider the stomach to be the seat of the emotions, as among some African and south-west Pacific Ocean societies that perceive the oral stage as medicinal.
Oral-stage fixation 
Psychologically, Sigmund Freud (1856–1939) proposed that if the nursing child’s appetite were thwarted during any libidinal development stage, the anxiety would persist into adulthood as a neurosis (functional mental disorder). Therefore, an infantile oral fixation (oral craving) would be manifest as an obsession with oral stimulation; yet, if weaned either too early or too late, the infant might fail in resolving the emotional conflicts of the oral, first stage of psychosexual development and he or she might develop a maladaptive oral fixation.
The infant who is neglected (insufficiently fed) or who is over-protected (over-fed) in the course of being nursed, might become an orally-fixated person. Said oral-stage fixation might have two effects: (i) the neglected child might become a psychologically dependent adult continually seeking the oral stimulation denied in infancy, thereby becoming a manipulative person in fulfilling his or her needs, rather than maturing to independence; (ii) the over-protected child might resist maturation and return to dependence upon others in fulfilling his or her needs. Theoretically, oral-stage fixations are manifested as garrulousness, smoking, continual oral stimulus (eating, chewing objects), and alcoholism. Psychologically, the symptoms include a sarcastic, oral sadistic personality, nail biting, oral sexual practices (fellatio, cunnilingus, analingus, irrumatio), et cetera..
Since Dr. Freud’s presentation of the theory of psychosexual development in 1905, no evidence has confirmed that extended breast-feeding might lead to an oral-stage fixation, nor that it contributes to a person becoming maladjusted or to developing addictions (psychologic, physiologic). The pediatrician Dr. Jack Newman proposed that breast feeding a child until he or she chooses to wean (ca. 2–4 years of age) generally produces a more psychologically secure, and independent person. Contradicting the Freudian psychosexual development concept of oral-stage fixation, the Duration of Breast-feeding and the Incidence of Smoking (2003) study of 87 participants reported no causal relation between the breast-feeding period and whether or not a child matures into a person who smokes.
- Mother Food for Breastfeeding Mothers, by Hilary Jacobson
- Jack Newman, MD, FRCPC (2005) Handout #21. Toddler nursing
- Raith, E (2003) Duration of Breast-feeding and the Incidence of Smoking Department of Psychology. Loyola University New Orleans. 
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