The health status of an individual, a community or a nation is affected by the interplay and integration of two types of environment—the internal environment of man himself and the external environment which surrounds him.
The internal environment pertains to ''each and every component part, every tissue, organ and organ system and their harmonious functioning within the body system". The health status of man is the outcome of a continual adjustment and readjustment between the internal and external environment.
Health hazards are caused due to lack of proper harmony between man and his environments. Man is living in a highly complicated environment which is getting more complicated as man is ' becoming more ingenious. The external environment consists of three main components—Physical, Biologic and Psycho-social, all closely related.
The term "physical environment" i3 applied to nonliving things and physical factors such as housing, water, air, soil climate, heat, light, noise, with which man is in constant interaction. In most developing countries, defective physical environment such as unsafe water, soil pollution with human wastes, poor housing continues to be the main health problem.
The biologic environment is the universe of living things which surrounds man, including man himself. The living things are the viruses, insect’s rodents, animals and plants. These are constantly working for their survival, and ' in this process some of them act as disease producing agents, reservoirs of infection and vectors of disease. When for any reason, the harmonious relationship is disturbed, ill health results.
The psycho-social environment includes a complex or social and psychological factors and conditions, cultural values, customs, habits, religion, education, occupation standard of living and community life. Man exposed to the social environment through literature, arts, press, radio and television. Indeed, man is very largely a product of his social and cultural environment which he shapes and is shaped by it.
Crime, violence, drug abuse and other forms of deviant behavior are due to psycho-social stress. From a psycho social point of view disease may be viewed as a ^maladjustment of the human organism to his psycho-social 'environment resulting from misperception, misinterpretation and misbehavior,
Although environment is divided into three components, it is the harmonious balance of the human individual integrated into his total environment, constitutes health. As a whole a stable and harmonious equilibrium between man and his environment is needed to reduce man's vulnerability to disease and to permit him to lead a more productive and satisfying life.