Mental health is "a state of well-being in which the individual realizes his or her abilities, can cope with the normal stresses of life, can work productively and fruitfully, and can make a contribution to his or her community", according to the World Health Organization (WHO). Mental health includes subjective well-being, perceived self-efficacy, autonomy, competence, intergenerational dependence, and self-actualization of one's intellectual and emotional potential, among others. From the perspectives of positive psychology or holism, mental health may include an individual's ability to enjoy life and to create a balance between life activities and efforts to achieve psychological resilience. Cultural differences, subjective assessments, and competing professional theories all affect how one defines "mental health". Some early signs related to mental health problems are sleep irritation, lack of energy, and thinking of harming yourself or others. Mental health, as defined by the Public Health Agency of Canada, is an individual's capacity to feel, think, and act in ways to achieve a better quality of life while respecting personal, social, and cultural boundaries. Impairment of any of these is a risk factor for mental disorders, which are components of mental health. Mental disorders are defined as health conditions that affect and alter cognitive functioning, emotional responses, and behavior associated with distress and/or impaired functioning. The ICD-11 is the global standard used to diagnose, treat, research, and report various mental disorders. In the United States, the DSM-5 is used as the classification system of mental disorders. Mental health is associated with several lifestyle factors such as diet, exercise, stress, drug abuse, social connections, and interactions. Therapists, psychiatrists, psychologists, social workers, nurse practitioners, or family physicians can help manage mental illness with treatments such as therapy, counseling, or medication. A mental illness is an illness of the mind. People with a mental illness may behave in strange ways or have strange thoughts in their view or the view of others. Mental illnesses can affect the day-to-day functioning of a person. Mental illnesses develop during the life of a person. This may be linked to genes and experience. What is considered a mental illness has changed over time. What is considered to be a mental illness may not be one in a different culture. The Diagnostic and Statistical Manual of Mental Disorders (DSM) by the American Psychiatric Association is used around the world. People with a mental illness sometimes have problems dealing with other people or struggle with daily functioning. Treatment and certain medications can help people with daily functioning. In some cases, mental illnesses change the way the brain works. Many conditions which affect the brain are not mental illnesses, as they do not change how people think: Neither epilepsy nor Parkinson's disease is a mental illness, yet both affect the brain. Mental health refers to the emotional well-being of a person. It is often viewed as an adult issue, but in fact, almost half of adolescents in the United States are affected by mental disorders, and about 20% of these are categorized as "severe." Mental health issues can pose a huge problem for students in terms of academic and social success in school. Education systems around the world treat this topic differently, both directly through official policies and indirectly through cultural views on mental health and well-being. These curriculums are in place to effectively identify mental health disorders and treat them using therapy, medication, or other tools of alleviation.