No one knows what causes a person to be addicted to the Internet, but there are several factors that have been proposed as contributing to Internet addiction. One theory concerns the mood-altering potential of behaviors related to process addictions. Just as a person addicted to shopping may feel a "rush" or pleasurable change in mood from the series of actions related to a spending spree— checking one's credit cards, driving to the mall, going into one's favorite store, etc.— the person with an Internet addiction may feel a similar "rush" from booting up their computer and going to their favorite web sites. In other words, some researchers think that there are chemical changes that occur in the body when someone is engaging in an addictive behavior. Furthermore, from a biological standpoint, there may be a combination of genes that make a person more susceptible to addictive behaviors, just as researchers have located genes that affect a person's susceptibility to alcohol.
In addition to having features of a process addiction, Internet use might be reinforced by pleasurable thoughts and feelings that occur while the person is using the Internet. Although researchers in the field of addiction studies question the concept of an "addictive personality" as such, it is possible that someone who has one addiction may be prone to become addicted to other substances or activities, including Internet use. People with such other mental disorders or symptoms as depression, feelings of isolation, stress , or anxiety, may "self-medicate" by using the Internet in the same way that some people use alcohol or drugs of abuse to self-medicate the symptoms of their mental disorder.
From a social or interpersonal standpoint, there may be familial factors prompting use of the Internet. For
Read more: http://www.minddisorders.com/Flu-Inv/Internet-addiction-disorder.html#ixzz3JdeuAzOA