Generally, laughter is related to a number of beneficial effects. Among humans, laughter is often expressed in babies as early as 4 months old. At this time, it usually occurs in response to the behavior of the caregiver. As the child grows older, the child begins to be joined in behaviors, which are intended to raise laughter in others. Ifs believed that the purpose of this development process is to establish social relationships in addition to gaining feedback as to what types of behavior should be strengthened or discouraged. Indeed, most laughter occurs when we are actually in social situations.

　　Aside from promoting social bonding, research has found that social laughing has also helped people physically. For example, it activates the release of endogenous opiates, chemicals which can reduce feelings of pain and have a relaxing effect, decrease the production of stress hormones (激素）and make the lung work better. Additionally, laughter has psychological benefits. It reduces stress, anxiety, tension, embarrassment, worry, frustration and anger. Ifs good for individuals like nurses, firefighters and soldiers because their work requires them to deal with terrible events or injuries.

　　What makes us laugh? Usually, the cause is something silly or negative (e.g. watching puppies play, violating a rule). It's also common for people to find humor in tragedies; in this respect, laughter serves as a coping mechanism (应对机制).

　　Some people like professional comedians intentionally set themselves up to the target of laughter. However, when laughter is directed at others, it's important that the generated laughter is not aggressive. Sometimes people laugh for the purpose of laughing at another or making another feel ashamed or stupid. In such instances, the laughter isn't performed in "good fun"，but at the cost of an individual who will be hurt by it. In these instances, the "laugher's" behavior is harmful.

Some people are particularly sensitive and have a fear of being laughed at or made to appear silly. This fear has been identified as gelotophobia (恐笑症).Although it isn't always pleasant to be the object of the joke, the effect this has on people ranges across