Mental illnesses are health conditions involving changes in emotion, thinking, or behavior. Mental illnesses are associated with distress and/or problems functioning in social, work or family activities. Mental illnesses affect 13% of the worlds population. Mental illnesses can develop through a blood relative, such as a parent or sibling. Mental illnesses occur from the interaction of multiple genes and other factors, such as stress, abuse, or a traumatic event. These things can influence, or trigger an illness in a person who has inherited susceptibility to it.