Peer pressure is feeling pushed by friends or classmates to think, look or act a certain way. Friends can influence what a person chooses to do, and a person can influence them too. Harvard psychologist Nancy Hill explains that peer pressure is not only an outside force. It can also be an internal force. It is spurred by a desire to belong. So a person may do something no one asked them to do. Some experts say "peer influence" is a better term than "peer pressure". It describes how teenagers' behavior is shaped by wanting to feel they belong to a group, and it is not always about doing something against your will. Hill says kids will always want to fit in with peers, so the useful question is what they are fitting into and whether it helps them or derails them.

Peer influence can be positive: it can push young people to become more assertive, try new activities or get more involved with school. Even peers a person has never met can be role models. One example is someone the same age who competes in a sport, plays a concert or leads a community project. Fitting in with friends is important during the teen years, so being influenced by others is completely normal, and sometimes people are even influenced to do good things like helping others. Prosocial behavior means actions meant to benefit others, such as volunteering, donating and sharing. Research shows young people also copy the prosocial behavior of their peers. Peer pressure can be a positive force: students at high schools where many classmates go on to college are more likely to go themselves. Peers often give each other good advice, and friends are quick to say when they think a friend is making a mistake.

Being in a peer group gives young people practice with social skills, like making new friends, building relationships and working out differences. During adolescence there is a period of social reorientation, in which young people spend less time with their parents and more time with same-age peers. Social worker Emma Petree says peer pressure gets really intense around the start of middle school. At that time a child's social circle moves to the forefront of their decision-making. Even young children often act differently in a group without grown-ups around than their parents expect, so pressure is not only a teen thing. Much of the similarity between friends was there before they became friends, because peers with similar interests and habits tend to gravitate toward each other. A clique differs from a group of friends: in a clique leaders decide who is in or out, but members of a friend group are free to hang out with others.

It is natural for people to compare themselves to their peers as they think about who they want to be or what they want to achieve. When people are unsure what to do in a social situation, they naturally look to others for cues about what is acceptable. Pressure can spread through a group: the people most easily influenced follow first, then others go along, thinking "everyone else is doing it, so they must know what they're doing." People who are low on confidence, or who tend to follow rather than lead, could be more likely to seek their peers' approval by giving in to a risky challenge. Responding to peer pressure is part of human nature, but some people are more likely to give in and others are better able to resist and stand their ground. Many young people struggle to understand how their peers see them and worry about being rejected if they do not fit in.

Young people may be more open to peer pressure partly because they worry more about what others think of them. Unlike younger children, they can imagine at an abstract level how others see them. Extension specialists point out that most peers are typically not making unhealthy choices, so "everyone is doing it" is often not true. In 1951 psychologist Solomon Asch set up a simple test. People judged which of three lines matched a target line, and the answer was always obvious. Asch's volunteers heard other people give a wrong answer. The confederates gave the wrong answer on 12 of the 18 trials, called the critical trials. On average about one third (32 percent) of the people on the critical trials went along with the group's clearly wrong answer. In Asch's experiment about three-quarters of the people went along with the wrong answer at least once, and about a quarter never did.

In Asch's control condition, there was no group pressure, and volunteers virtually never made mistakes. This shows the line task was easy and the wrong answers came from the group. In Asch's experiments a single dissenting person cut conformity by about 80 percent, so having one ally greatly reduced going along with the group. A 1980 British replication of Asch's study found almost no conformity, suggesting Asch's high rates partly reflected the 1950s American setting. Saying no can feel like it has a high social cost. Having a friend or two who feel the same and will stand beside a person can take some of the social pressure off. One study of young people divided a pool of coins between themselves and a group. Online peers gave likes, and one group liked donating while the other liked keeping coins. In that coin game, changes in generous behavior depended on which choices the peer group liked, showing that peers can both decrease and increase prosocial behavior.

In one classroom study, students estimated the number of animals in an image, then saw a classmate's answer and could change their own. In that study, young people changed their answers more when the other person was a friend than when they were a distant classmate. In a risk-perception study, young people were more influenced by same-age peers' opinions than by adults' opinions, while children and adults were more influenced by adults' opinions. Another study, of 136 students aged 11 to 14, tested whether copying a peer changes how much time a teen volunteers for a charity. In the charity study, a made-up peer donated an average of 8 minutes to one half of the young people and 2 minutes to the other half, and the young people then chose how much time to give. Young people who saw a very generous peer donated more minutes afterwards, and young people who saw a less generous peer donated fewer, though all began with similar amounts.

In a study of 456 Dutch young people, older teens were more likely than younger teens to follow an example of a peer donating money to charity. Amsterdam researcher Andrea Gradassi says learning from others is adaptive: watching what successful peers do helps people avoid costly trial and error. Researchers say findings about young people and charity show that adapting to peer behavior can sometimes be a good thing, even though people are often taught that peer conformity is bad. Developmental researchers argue that the teen brain is highly malleable and particularly oriented towards the social world, which may explain heightened susceptibility to social influence. A review of brain studies describes a maturational imbalance model. Control systems in the front of the brain mature slowly. Reward and social-emotional circuitry is hyperactive in adolescence. Social-brain regions such as the temporoparietal junction and posterior superior temporal sulcus help us notice social information like facial expressions and social rules, and motivate prosocial behavior.

Most evidence that social rewards are extra strong in adolescence comes from animal studies: teen rats find playing with other rats more rewarding than adult rats do. Human young people show increased brain activation in fronto-striatal regions to rewarding social stimuli and also to negative social stimuli, so young people may be hypersensitive to all social stimuli, not only social rewards. An fMRI scan uses the magnetic properties of blood to track changes in blood flow, and more blood flow to a brain region means that area is being used. A 2011 experiment with brain scans had young people, young adults and adults make decisions in a simulated driving task, once alone and once while peers watched from an adjacent room. In the 2011 brain-scan study, the presence of peers raised risk taking among young people but not adults. Young people had more activity in reward-related brain regions, including the ventral striatum and orbitofrontal cortex, when peers were watching, and that activity predicted later risk taking.

The researchers read the result as peers making risky choices feel more rewarding, and not as peers turning off self-control, because cognitive-control activity did not vary with social context. Researchers say peers and parents can both support young people's positive adjustment, and peers more often reinforce family values than work against them. Adults sometimes picture peers as one united front of dangerous influence, but extension researchers call that inaccurate: more often than not, peers reinforce family values. Experts say it helps to explain values, and not only say "don't do this", so young people can make decisions for themselves and feel independent. The Search Institute lists positive peer influence, and the ability to resist negative peer pressure and dangerous situations, among the developmental assets that help young people. One skill that helps is weighing costs and benefits: looking at both the negative and positive sides of a decision before choosing.

A person in a clique can ask whether they want to be part of the group because they want to feel accepted or because they actually share its values. It helps to deal with peer pressure before it happens by talking through possible scenarios and role-playing what to say. Hill suggests practicing scenarios where a feeling might be tested and helping a young person think through a response that feels natural to them. Kids do not always know what to say, or how to say no and keep a friend, so practicing the words at home helps. A young person is more likely to ask a trusted adult for help if they know they will not get into trouble for asking, so adults are advised to praise the choice to ask. Friends from many places, such as sports, clubs and family activities, give a person more people to turn to if one friendship goes wrong.

A secret code word with a parent is a way to ask for help and leave a spot without being embarrassed in front of friends. A parent or other adult can step in when peer pressure gets too hard for a kid to handle. A grown-up you trust can help.

Words to know

• clique: tight group
• prosocial: helping others
• adaptive: helpful
• replication: a repeat study
• malleable: easy to shape