Mental health refers to our emotional, psychological, and social well-being and how we think, feel and act. It affects how we handle stress and relate to others. Mental illness involves changes in emotion, thinking or behavior that interfere with daily life. Factors that influence mental health include neurobiological factors, cultural factors, psychosocial factors like ego function and defense mechanisms, and stress and illness. A normal person may not always have good mental health but can still function daily, while those with mental illness have daily functions affected.