A mental disorder is an illness that affects people’s emotions, thoughts, or behavior and produces a negative effect on their lives and/or the lives of their families.
One way to define unusual behavior is to ask whether the doings (activities) or the manners cause damage to the person’s life. The more the person’s behavior disturbs his occupational, interpersonal and social functioning, the more likely it is to be considered as a sign of emotional or mental deformity. When several such behaviors or indications occur together, they may constitute a psychosomatic or mental disorder.
Symptoms of mental disorders are caused by biological or genetic factors such as biochemical imbalances, brain defects, and genetic inclinations.