Nidanam in Ayurveda is an ayurvedic terminology that is the cause or factor by which pathogenesis occurs in the body. This is also called `hetu` or `kaaran`. There might be only one cause for the disease that comes from any one of the three doshas. This may take place due to consumption of unsuitable objects that interferes with the internal homeostasis of the body. To understand Nidanam or the cause of the diseases one have to take in consideration how the different doshas enact to create a disease and how the unsuitable objects are the causative agent for the imbalance of human mind and body.

Nidanam can be classified in different ways, like Viprakrista nidanam, Vyabbhicharika Nidanam and Pradhanika Nidanam. In other way Nidanam is classified as Asatmyendriyardha Samyoga, Pragyapradh and Parinama. There is another category of Nidanam, by which it is categorized into three classes-dosha Nidanam, Vyadhi Nidanam, Ubhaya Nidanam. Nidanam can also be divided into two classes-Utpaadaka and Vyanjaka. The Baajhya Hetu or external cause and Abhayantar Hetu or Internal Cause are other two categories of Nidanam.

Doshas can be again classified into two categories viz Anubandha or the Subordibnate Dosha and Anubandhya or the main dosha. There are some exceptions like Upadrava (complication) which is an anubandha dosha. The subordinate doshas are cured when the main disease is treated. But upadravas are to be treated first before curing main diseases.

Nidanam are further classified into many categories. These are Kshaya or decrease, sthanaam or normal and Vriddi or increase. When Ama is involved the Nidanam is again classified into Saam and Niraam. Nidanam is again classified into two kinds. These are Nija and Agantuka.

Sannikrista Nidanam or the Immediate Cause: This is the immediate or the instant cause like improper food or food consumed at the wrong time or wrong season. This is the immediate cause of Doshas. Chaya (increase) or Prasma (subsidence) are not considered here. As the improper food is taken, the immediate cause of the disease is obvious.

Vipakrista Nidanam or the Distant Cause: This is the remote or distant cause of the disease. For example if the Kapha is accumulated in the Hemant Ritu (early winter) and Kapha disease occurs at Basanta ritu (Spring) it can be termed as Vipakrista nidanam. Here there is a certain amount of time interval between the cause and the effectiveness of the disease. Kapha Dosha is main example of this kind as Kapha accumulates in early winter and disease occurs in spring.

Vyabbhicharika or the Weak Cause: this is subservient or the weak cause which is unable to cause a disease by itself as the body`s own immunity system is very strong here. For instance, a germ may enter the body but it may not produce a disease at all and this type of cause is called Vyabbhicharika Nidanam.

Pradhanika or Predominant Cause: It is the patent or predominant cause. For example, when Visha or poison is administered to the body, the treatment for elimination of Visha is more important than to cure the symptoms or deranged Dosha, that is caused by Visha. Therefore Visha is referred to as Pradhanika.

Astamyendriyardha Samyoga: There are five senses in human body through which it makes contact with the external world. By incompatible correlation of the senses the disease can be caused. The relationship may be of three kinds- Heenyoga or deficient use, Atiyoga or excessive use, mithya yoga or perverted use. For example one can eat or drink too much or too little or unsuitable articles due to improper relationship with the example.

Pragyapradh : It is the perverted use of mind or in other words lack of understanding.This faults can be exhibited in three possible ways-Sareeraka or body , Vachika or speech and Manasika or mind. This are the causes of the diseases due to faulty understanding and causes of abnormality of balance of Dhatus.

Parinama : It occurs due to some abnormalities of seasons i.e. heat, cold or rain. If these factors become abnormal they may cause disease by upsetting the normal equilibrium of the doshas. Thus too severe or too mild seasons, lack of raining or excessive raining and prevalence of winter in the summer or vice versa may enhance the Doshas.

Dosha Nidanam: This is the imbalance, accumulation or derangement of Doshas that is caused by influence of ritus or seasons. For instance, Hemant (early winter) and Sishir (winter) ritu has the madhur rasa prevailing that interferes with the unbalance of doshas.

Vyadhi Nidanam: When it is confirmed that by certain deeds the person will have diseases it is called Vyadhi nidanam. For example when a person eats clay or earth he or she might have Pandu Roga(anemia).

Ubhaya Nidanam: The cause is single but results in two ways of suffering. For example when one travels long distance on horse or camel, it enhances Vata dosha as well as Vatarakt (gout) also takes place due to increase circulation of blood on specific points.

Utpaadaka Nidanam: this means susceptible cause. For example the Madhur Rasa generated in Hemant and Sisir Ritu may be predisposing factor of Kapha dosha.

Vyanjaka Nidanam: it implies present or existing cause. For example accumulated kapha in Hemant ritu melts in Basant Ritu because of sun`s heating and results in Kapha related disorder in Basant Ritu. Baahya Hetu:

Vata Dosha : excessive exercise, Langahan Karma. Fall from heights like tree or anything high, fracture, tuberculosis, cold, terror or over emotional stress can be accounted within Vata dosha. This dosha is increased due to consumption of Ruksh (dry), Kashaya(astringent), Katu (bitter) and tickt (pungent) substances when they are taken in Varsha Ritu (rainy season) causes aggression of Vata dosha in morning and evening.

Pitta Dosha: Consumption of katu(bitter), amal(sour), lavan (salty) and tikshan (exciting food) increases Pitta dosha. The other causes of enhancement of Pitta Dosha are anger, fasting, taking sun bath, indulgence in sex. Consumption of alsi, curd, vunegar and kanji also increases Pitta dosha. In sharad ritu (autumn) and in Grisham Ritu (summers) the pitta gets aggravated at midnight and midday.

Kapha Dosha : consumption of Guru(heavy) food, Madhur rasa (sweet). Snigdh(oily), ruksh(dry), products made out of sugarcane like sugars, jaggery etc, curd, milk and other dairy products. Kapha is aggravated in hemant ritu (early winter), shishir ritu (winters) in early morning and in basant ritu (spring).

The Abhayantar hetu is the internal causes like Vata, Pitta and Kapha. There is also involvement and indulgence of the seven dhatus including rasa, rakta, mamsa, meda, asthi, majja and shukra. There are two types of doshas in this category :

Prakruti Dosha(seasonal dosha): In different ritus different doshas are aggravated, like in Vasant ritu Kapha dosha, in sharat ritu the pitta dosha and in varsha ritu the vata dosha are enhanced.

Vikriti Dosha : Fever caused by pitta dosha and Kapha dosha in Vasant and sharat ritu can be easily cured but fever caused by Vata is difficult to cure. The prakriti doshas are all under Vikriti dosha as they also occur under certain circumstances.

Ama: When Jatharagni (digestive fire) is not ignited, the food consumed is partially digested and the rest remains in the amashya(stomach) in the form of polluted rasa dhatus and this is called Ama. It can be compared with the toxins that produced due to indigestion.

If the Dosha is immature and affected by ama dosha then it is Saam dosha (immature dosha). On the other hand when the dosha is not affected by ama dosha it is called Niraam dosha (nature dosha). In Saam dosha pachan (digestion) and Langahan karma (effective reduction) is needed whereas in Niraam dosha shaman karma (to settle down dosha at the place of action) must be performed.

Diseases are of two types -Nija and agantuka and both are associated with the manna (mind) and sthool sharir(body). Maharishi sushrut has divided diseases into three categories, which are:

1. Aadhyaatmik Roga-diseases originated inside the body, this can be manas (mental) or sharirika (bodily) diseases.

2. Aadhibhowtika Roga- caused by bhowtik or external factors like injury, trauma etc.

3. Aadhidaivik Roga- the causes of this type of disease is beyond human control i.e. natural calamities like earthquake, volcanoes etc.

Agantuka causes includes three types, these are -
1. Abhichara- casting of evil sources and unsoulful purposes.

2. Abhishapa- pronouncing curse on somebody or something

3. Abhishanga- the invasion of invisible elements like Bhutas and Grahas.