Siddha science considers nature and man as essentially one. Nature is man and man is nature. Man is said to be the microcosm and Universe is the macrocosm because what exists in the world exists in man. Man is nothing but a miniature world containing
the five elements of the various principles which constitute the minerals, vegetables and the animal kingdom. According to Siddha medical science, the Universe originally consisted of atoms which contributed to the five basic elements, viz., earth, water,
fire, air and sky which correspond to the five senses of the human body and they were the fundamentals of all the corporeal things in the world.
A close relationship is found to exist between the external world and the internal system of man. Siddhars
(practitioners of Siddha) maintain that the structure of the human body is a miniature world in itself. Man consumes water and food, breathes the air and thus maintains the heat in the body. He is alive on account of the life force given by ether. The earth is the first element which gives fine shape to the body including bones, tissues, muscles, skin, hair etc. Water is the second element representing blood, secretions of the glands, vital fluid etc. Fire is the third element that gives motion, vigor and vitality to the body. It also helps digestion, circulation and simulation besides respiration and the nervous system. Above all, ether is the characteristic of man's mental and spiritual faculties.
Siddha system of medicine is based on Saiva Siddhantha. Siddha is a Tamil word that is derived from its root 'chit' which means perfection in life or "heavenly bliss".