Nearly half of the world's population is affected by mental illness which impacts self-esteem, relationships and ability to function. Good mental health allows one to realize their abilities and cope with stress, while poor mental health prevents a normal life. Mental health involves well-being and functioning well, while mental illness affects thinking, feelings and behavior. Risk factors for mental disorders include genetics, age, toxins, infections, and family/social problems. Both physical and mental health problems interact and influence each other. Prevention strategies target promotion, early intervention, treatment and social support/rehabilitation.