Disease is the state of body and mind in which a person experiences discomfort, pain and injury. The fundamental cause of disease is the imbalance of the three doshas - Vata, Pitta and kapha. When the three doshas are balanced the body experiences health and the state of imbalance or disequilibrium is disease. The imbalance may be due to an increase or decrease in one, two or all the three doshas. The classification of disease in Ayurveda is done in various ways.

Ayurvedic Concept of Disease
The Ayurvedic concept of disease explains pathological condition in terms of doshas, dhatus and malas. The Ayurvedic concept of disease defines two terms, vikruti and prakruti. Vikruti is the abnormal or diseased condition of the body while prakruti refers to the normal physiological and mental state.

Causative Factors of a Disease
According to Ashtang Ayurveda, the causative factors of a disease are an imbalance in any or more of the three doshas (vata, pitta and kapha), the seven dhatus (rasa, rakta, mansa, meda, asthi, majja and shukra), agni and the three malas (mutra, purisha and sweda). The imbalance may be caused by the following conditions: "Asatmendriyarth Samyog", Aama, Pradnyaparadha and Parinama. "Asatmendriyarth Samyog" stands for improper or too much exploitation of the sense organs of vision, sound, smell, sense and touch.

Classification of disease in Ayurveda
One of the methods of classification of disease in Ayurveda is on the basis of the causative factors. Classified thus, we have three types of diseases: Adhyatmika diseases, Adhibhautika diseases and Adhidaivika diseases. Adhyatmika diseases have their source within the body, and may be further divided into hereditary diseases, congenital disease, and diseases caused by one or more of the doshas or body tissues. Adhibhautika diseases have their source outside the body and incorporate such things as injuries from accidents or mishaps, and according to modern terms, invasions by germs, viruses, and bacteria. Adhidaivika diseases are believed to spring from supernatural sources. This category includes diseases whose exact cause has not yet been found out. It includes ailments cropping up from providential causes, planetary influences, curses and seasonal changes. A more practical classification of disease convenient for treatment classifies the diseases into seven categories. Aadi- bala pravritta refers to those diseases that are transmitted through genes. Human beings are genetically predisposed to fall prey to such diseases. Janma- bala refers to those diseases that are present in the body from birth. Dosha -bala incorporates those diseases that affect the body when the body is suffering from an imbalance of the three doshas, vata, pitta and kapha. Under the category of Sanghata-bala fall those diseases, which are caused by trauma, both physical and mental. Kaala - bala refers to those diseases caused by seasonal changes. Daiva -bala signifies those diseases, which are caused by Gods or spirits. Svabhaava -bala incorporates those diseases that are a part of the natural change of the body with the passage of time. It includes aging and withering of the body.

The classification of disease can also be done as nija, agantuja, sharirik and manasik. Nija refers to endogenous diseases caused by disorder in the doshas. Agantuja stands for exogenous diseases that are caused by external reasons like injuries. Here too the imbalance of doshas does occur but only after the condition of the disease becomes pathological. The diseases caused by physiological disturbances are called sharirik diseases and those, which are a result of psychological disturbances, are known as manasik diseases. Ayurveda also gives the classification of disease according to their curative measures. Thus classified diseases can be Sukhasadhya, Kruchrasadhya, Yapya and Asadhya. Those diseases, which get cured very easily, are categorised under Sukhasadhya. Kruchrasadhya diseases take a lot of time to cure. Those diseases, which recur when the treatment is stopped, fall under the category of Yapya. Asadhya signifies those diseases that are incurable.

Thus, classification of disease is done in many ways in Ayurveda. Such an intensive classification system facilitates proper treatment of diseases.

Parinama in Ayurveda
Parinama refers to abrupt environmental changes, which makes the body vulnerable to disease.Parinama or kala also refers to the effects of time, and the natural physical transformation that are affected as time progresses. In short kala or parinama is defined as "being out of harmony with the rhythms and cycles of Nature". Ayurveda talks about several important cycles at a macrocosmic level, which in turn affects the physiological conditions of human beings.

Pradnyaparadha in Ayurveda
Pradnyaparadha is the improper use of intellect or wisdom that makes the body vulnerable to ailments.This means those thoughtless actions, which are undertaken without determining whether those actions will be detrimental to the proper functioning of the body. These actions may be verbal, mental or physical. The actions stimulated by pradnyaparadha worsen the tridosa system in the body and stimulates the gunas of rajas and tamas creating a pathway through which disease can enter the body.