Health is generally defined as being "a state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity". This definition is used by the World Health Organization (WHO) since 1948. In 1986, the WHO, in the Ottawa Charter for Health Promotion, said health is "a resource for everyday life, not the objective of living. Health is a positive concept emphasizing social and personal resources, as well as physical capacities". Classification systems such as the WHO Family of International Classifications (WHO-FIC), which is composed of the International Classification of Functioning, Disability, and Health (ICF) and the International Classification of Diseases (ICD) also define health.Overall health is achieved through a combination of physical, mental, emotional, and social well-being.Aspects of health Physical healthPhysical fitness refers to good body health, and is the result of regular exercise, proper diet and nutrition, and proper rest for physical recovery.A strong indicator of the health of localized population is their height or weight, which generally increases with improved nutrition and health care. This is also influenced by the standard of living and quality of life. Genetics also plays a major role in people's height. The study of human growth, its regulators, and implications is known as Auxology. Mental healthain article: Mental healthMental health describes either a level of cognitive or emotional well-being or an absence of a mental disorder. The World Health Organization defines mental health as "a state of well-being in which the individual realizes his or her own abilities, can cope with the normal stresses of life, can work productively and fruitfully, and is able to make a contribution to his or her community”. However, despite official definitions, the term mental health, and the question of whether or not an individual is 'mentally well', remains a subjective assessment. Determinants of healthMain article: Social determinants of healthThe LaLonde report suggested that there are four general determinants of health including human biology, environment, lifestyle, and healthcare services. Thus, health is maintained and improved not only through the advancement and application of health science, but also through the efforts and intelligent lifestyle choices of the individual and society.A major environmental factor is water quality, especially for the health of infants and children in developing countries.Studies show that in developed countries, the lack of neighborhood recreational space that includes the natural environment leads to lower levels of neighborhood satisfaction and higher levels of obesity; therefore, lower overall well being. Therefore, the positive psychological benefits of natural space in urban neighborhoods should be taken into account in public policy and land use. Maintaining healthMain article: Self careAchieving health and remaining healthy is an ongoing process. Effective strategies for staying healthy and improving one's health include the following elements: Nutritionain article: NutritionPersonal health depends partially on the social structure of one's life. The maintenance of strong social relationships is linked to good health conditions, longevity, productivity, and a positive attitude. This is due to the fact that positive social interaction as viewed by the participant increases many chemical levels in the brain which are linked to personality and intelligence traits. Sports nutritionMain article: Sports nutritionSports nutrition focuses the link between dietary supplements and athletic performance. One goal of sports nutrition is to maintain glycogen levels and prevent glycogen depletion. Another is to optimize energy levels and muscle tone. An athlete's strategy for winning an event may include a schedule for the entire season of what to eat, when to eat it, and in what precise quantities (before, during, after, and between workouts and events). HygieneMain article: HygieneHygiene is the practice of keeping the body clean to prevent infection and illness, and the avoidance of contact with infectious agents. Hygiene practices include bathing, brushing and flossing teeth, washing hands especially before eating, washing food before it is eaten, cleaning food preparation utensils and surfaces before and after preparing meals, and many others. This may help prevent infection and illness. By cleaning the body, dead skin cells are washed away with the germs, reducing their chance of entering the body.Prolonged psychological stress may negatively impact health, such as by weakening the immune system and mind. Stress management is the application of methods to either reduce stress or increase tolerance to stress. Relaxation techniques are physical methods used to relieve stress. Psychological methods include cognitive therapy, meditation, and positive thinking which work by reducing response to stress. Improving relevant skills and abilities builds confidence, which also reduces the stress reaction to situations where those skills are applicable.Reducing uncertainty, by increasing knowledge and experience related to stress-causing situations, has the same effect. Learning to cope with problems better, such as improving problem solving and time management skills, may also reduce stressful reaction to problems. Repeatedly facing an object of one's fears may also desensitize the fight-or-flight response with respect to that stimulus—e.g., facing bullies may reduce fear of bullies.Prolonged hours of surfing on the Internet is a major concern that can affect the eyes significantly. White backgrounds on computer screens with a viewing distance of less than 14 inches is known to increase strain, mental fatigue and temporary di-chromatic visions in a normal healthy human being. Trying to opt for black or any non-white backgrounds can help in reducing eye strain in front of PCs. Health careain article: Health careSee also: #Public healthHealth care is the prevention, treatment, and management of illness and the preservation of mental and physical well being through the services offered by the medical, nursing, and allied health professions. Workplace wellness programsMain article: Workplace wellnessWorkplace wellness programs are recognized by an increasingly large number of companies for their value in improving the health and well-being of their employees, and for increasing morale, loyalty, and productivity. Workplace wellness programs can include things like onsite fitness centers, health presentations, wellness newsletters, access to health coaching, tobacco cessation programs and training related to nutrition, weight and stress management. Other programs may include health risk assessments, health screenings and body mass index monitoring. Public healthMain article: Public healthPublic health is "the science and art of preventing disease, prolonging life and promoting health through the organised efforts and informed choices of society, organizations, public and private, communities and individuals." It is concerned with threats to the overall health of a community based on population health analysis. The population in question can be as small as a handful of people or as large as all the inhabitants of several continents (for instance, in the case of a pandemic). Public health has many sub-fields, but is typically divided into the categories of epidemiology, biostatistics and health services. Environmental, social and behavioral health, and occupational health, are also important fields in public health.The focus of public health intervention is to prevent rather than treat a disease through surveillance of cases and the promotion of healthy behaviors. In addition to these activities, in many cases treating a disease can be vital to preventing it in others, such as during an outbreak of an infectious disease. Vaccination programs and distribution of condoms are examples of public health measures. Role of science in healthMain article: Health scienceHealth science is the branch of science focused on health, and it includes many subdisciplines. There are two approaches to health science: the study and research of the human body and health-related issues to understand how humans (and animals) function, and the application of that knowledge to improve health and to prevent and cure diseases. SourcesHealth research builds primarily on the basic sciences of biology, chemistry, and physics as well as a variety of multidisciplinary fields (for example medical sociology). Some of the other primarily research-oriented fields that make exceptionally significant contributions to health science are biochemistry, epidemiology, and genetics. ApplicationApplied health sciences also endeavor to better understand health, but in addition they try to directly improve it. Some of these are: biomedical engineering, biotechnology, nursing, nutrition, pharmacology, pharmacy, public health (see above), psychology, physical therapy, and medicine. The provision of services to maintain or improve people's health is referred to as health care (see above).