Unani system of medicine recognizes the influence of surroundings and ecological conditions on the state of health of human beings. This system aims at restoring the equilibrium of various elements and faculties of the human body. It has laid down six essential pre-requisites for the prevention of diseases and places great emphasis, on the maintenance of proper ecological balance and, on the other, on keeping water, food and air free from pollution. These essentials, known as 'Asbab-e-Sitta Zarooriya' and are as follows, air, food and drinks, bodily movement and repose, psychic movement and repose, sleep and wakefulness, and exertion and retention etc. In this article we will discuss on these six essentials, how they play an important role in preservation of health and how these are correlated with tabiat in maintenance of health.