For any organism, health is a dynamic balance. It is a state of balance: energy and matter are input and output in a balanced way (even allowing growth). Health also means the expectation of continuing to live. For animals with feelings, such as humans, health has a broader concept. Health and unhealthy are not absolute opposites, but a relative transitional state. The Constitution of the World Health Organization defines health as: "Health is not just a disease or sudden death.
Health belongs to the medical field, and its core is environmental sanitation, nutrition, disease prevention and public health affairs.
People can investigate these aspects to help assess health. In some countries, health includes the management of physical condition after meeting more basic food, shelter and basic medical security. Many of these practices are in pursuit of happiness, but in fact they are committed to controlling the side effects of wealth.
Since the middle class appeared in the industrialized world in the late19th century, the concept of health has gradually become popular in western countries. Since then, a new and prosperous public has time and resources to pursue happiness and other forms of self-improvement. Many early consumer goods, from cornflakes to mouthwash, originated from the growing public interest in health. Health can be maintained through scientific tests or practices, such as checking cholesterol, blood pressure and glucose. It also includes some controversial practices, such as avoiding certain foods and injecting certain vitamins or alternative drugs.