The exact cause of hypochondriasis is not known. Factors that might be involved in the development of the disorder include:
- A history of physical or sexual abuse
- A history of having a serious illness as a child
- A poor ability to express emotions
- A parent or close relative with the disorder. Children might learn this behavior if a parent is overly concerned about disease and/or overreacts to even minor illnesses.
- An inherited susceptibility for the disorder
Information was found on http://www.webmd.com/mental-health/hypochondriasis
There is plenty more information on this site, if you need more information.