The main principle of ayurveda is as follows :-
“Swasthasya Swasthya Rakshanam Aaturasya Vikara Prashamanam Cha”
This principle means to rejuvenate and preserve the health of the healthy and to alleviate the disease of the sick.
Ayurveda was brought to humanity by Rishi Bhardwaj from Indra. According to ayurveda, the healthy is called prakriti and unhealthy is called vikriti. Imbalance of dhatus is called disease (vikriti) and the balance of dhatus is called health (prakriti). Health is joy and disease is sorrow. In ayurveda practice, the imbalance of the doshas which are vata, pitta, kapha has been popularly named disease. So there are two statements seemingly against each other as written above but fundamentally they are the establishment of the same meaning. The etymology of dhatu has been said to be so – what contains the body is called dhatu. With this meaning, prakrit vata, pitta and kapha, evenly distributed rasa (plasma), rakta (blood), mamsa (muscle), medas (fat), asthi (bone), majja (marrow/nerve) and shukra (reproductive tissue), and sweat, excreta, and urine are also called dhatu. So the imbalance of dhatus can be understood as the imbalance of three doshas, seven dhatus and excreta, urine and sweat etc. Dhatus have been classified into two areas – Prasadadhatu and Maladhatu.
Whatever pollutes the body is called “Dosha”. In this meaning, vikrit doshas including vata, pitta, kapha, vikrit dhatu including rasa, rakta, mamsa, medas, asthi, majja and shukra, and vikrit excreta, urine and sweat are also considered to be dosha. So the imbalance of doshas means the imbalance of vata, pitta, kapha, seven dhatus, and excreta, urine, sweat etc and this is what is called disease. In reality the three doshas vata, pitta, kapha are considered to be doshas. The word 'dosha' is used in the treatment as opposed to the seven dhatus, as similar to how when somebody gets burnt by hot milk the statement said is 'burnt by milk'. Fundamentally burning is the action of fire, but the quality of fire is transmitted in the milk so hot milk is considered as fire in practical usage and 'burnt by milk' is popularly used to express.
According to Sushruta, disease has been defined as union with sorrow through any means. This sorrow is of two types – bodily and mental. There is visibly no sorrow in diseases like moles, worms or some skin disorders but due to changes in skin there is mental disturbance involved in it. In Patanjali-yogdarshan the symptom of sorrow is adverse or contrary feelings and the symptom of joy is feelings in accordance. A mole in the body gives contrary feelings, that is why it is also considered to be a vikara or problem.
Ayurvedic medicine brings about balance in the three doshas vata, pitta, kapha and alleviates the symptoms of disease or the disease itself. According to ayurveda, the definition of a healthy person is as follows -
“Sam Dosha Sam Agni Sam Dhatu Mala Kriya
Prasanna Atman Indriya Manaha Swastham Ity Abhidhiyate”
This means that a balanced state of the main elements of our body which are dosha and dhatu, adequate digestion which is agni, proper excretion which is mala kriya, blissful condition of the atman which is soul, satisfied senses which is indriya, and a happy state of mind which is manaha when encompassed in a person, then the person is called as a healthy person.