Social rejection
Social rejection exists in a variety of different forms and includes both interpersonal rejection or peer rejection, and romantic rejection. It occurs when an individual is deliberately excluded from a social relationship or social interaction. A person can be rejected on an individual basis or by an entire group of people. Furthermore, rejection can occur either actively by bullying, teasing, or ridiculing, or passively by ignoring the rejected person (e.g. the silent treatment). Rejection can be perceived when it is not actually present.
Because humans are social creatures, and because it is impossible to interact with everyone all the time, some level of rejection is an inevitable part of life. However, rejection can become a problem when it is excessive, when the relationship is important, when the rejection is by an entire group, or when the individual is particularly sensitive to rejection.
The experience of rejection can potentially lead to a number of adverse psychological consequences such as loneliness, reduced self-esteem, aggression, and depression. It can also lead to feelings of insecurity and a heightened sensitivity to future rejection.

# Need for acceptance
Rejection can be emotionally painful because of the social nature of human beings and our basic need to be accepted in groups. Abraham Maslow and other theorists have suggested that the need for love and belongingness is a fundamental human motivation. All humans, even introverts, require a certain amount of social acceptance and interaction to be psychologically healthy. Being a member of a group is important for social identity, which is a key component of the self-concept. Rejection by an entire group of people can have especially adverse effects, particularly when it results in social isolation.
Social psychological research confirms the motivational basis of the need for acceptance. Specifically, fear of rejection can lead to conformity to peer pressure (sometimes called normative influence), and compliance to the demands of others. Our need for affiliation and social interaction appears to be particularly strong when we are under stress.

# Rejection in childhood
Rejection has been measured in children using sociometry and other peer rating methods. Studies typically show that some children are popular, receiving generally high ratings, many are in the middle, with moderate ratings, and a minority of children are rejected, showing generally low ratings. Most research in this area examines children who are generally rejected by the majority of their peers.
Peer rejection, once established, tends to be stable over time, and thus difficult for a child to overcome.
Rejected children are likely to have decreased self-esteem, and to be at greater risk for internalizing problems like depression. Some rejected children display externalizing behavior and show aggression rather than depression. This research is largely correlational, but there is evidence that aggressive behavior in children precedes and may contribute to subsequent rejection experiences.

# Rejection in the laboratory
The short-term effects of rejection have been studied in the social psychological laboratory. One common experimental technique is the "ball tossing" paradigm, which involves a group of three people tossing a ball back and forth. Unbeknownst to the actual participant, two members of the group are working for the experimenter and following a pre-arranged script. In a typical experiment, half of the subjects will be excluded from the activity after a few tosses and never get the ball again. Only a few minutes of this treatment are sufficient to produce negative emotions in the target, including anger and sadness. This effect occurs regardless of self-esteem and other personality differences. A computer version of the task known as "cyberball" has also been developed and leads to similar results. Surprisingly, people feel rejected even when they know they are only playing against the computer.
Gender differences have been found in these experiments. In one study, women showed greater nonverbal engagement whereas men disengaged faster and showed face-saving techniques, such as pretending to be uninterested. The researchers concluded that women seek to regain a sense of belonging whereas men are more interested in regaining self-esteem.

# Romantic rejection
In contrast to research on childhood rejection, which focuses primarily on rejection by a group, research on romantic rejection focuses on a single individual rejecting another.
In teenagers and adults, romantic rejection occurs when a person refuses the romantic advances of another or unilaterally ends an existing relationship. Unrequited love is a common state in youth, but mutual love becomes more typical as people get older.
One reason why romantic rejection is so common in society is a tendency called falling upward. People generally desire mates that are higher but not lower than themselves on such characteristics as status and physical attractiveness. When someone falls in love with a person who has aspirations that are higher, that love is less likely to be reciprocated, potentially leading to rejection.

# Rejection sensitivity
Individuals differ widely in their level of rejection sensitivity. According to Geraldine Downey and her colleagues at Columbia University, rejection sensitivity is a tendency to anxiously expect, readily perceive, and over-react to social rejection. For those who have a high level of rejection sensitivity, an ambiguous social interaction may be perceived as rejection. This can lead to defensiveness and self-fulfilling prophecies.
Individual differences in rejection sensitivity are believed to be the result of previous rejection experiences, particularly childhood experiences with parents and peers. Attachment theory suggests that rejection from parents could lead to rejection sensitivity. One study found that rejection sensitivity in adulthood was related to teasing experiences during childhood, but not the amount of support received from childhood friends. This indicates that friendships are not enough to protect children from rejection experiences.