Though there is no universal definition of childhood bullying, the term is often used to describe when a child repeatedly and deliberately says or does things that causes distress to another child. Research shows that persistent bullying can cause depression and anxiety and contribute to suicidal behaviour.

This paper will bring into focus some studies done by the Department of Mental Health that show that the impact of bullying in childhood can cause depression, anxiety and especially OCD in adult. Also strongly contributes to bullying in suicidal behaviour.

The study involved 177 children aged 9–15 years old and were followed until they were 19–25 years old. The study ended in 2013. The subjects in this group were found to be 6 times more likely to have a serious physical illness, or develop a psychiatric disorder in adulthood than those who were not involved in bullying.

Another study in 2014 found that the negative effects at social, physical and mental health of childhood bullying are still evident up to 40 years later. Victims of bullying are 6 times more likely to have a physical nature of infectious diseases, to burn regularly or develop a mental disorder in adultery more than those not exposed to bullying, 11 times more likely to develop anxiety disorder but especially obsessive-compulsive disorder.

Some experts think that bullying results in a kind of “toxic stress” that affects children's physiological responses, possibly explaining why some victims of bullying go on to develop health problems.