Agni in Ayurveda (आयुर्वेदे अग्निः)
Agni ( अग्निः) is an important vital entity in Ayurveda. Its chief function is to assimilate or transform. It has a potential to convert the biologically distinct substances into the form which can be used up by the body tissues for their growth and nourishment. This action happens at multiple different sites in the body and is responsible for many life processes. Any fluctuation in the strength of agni leads to imbalances in the level of doshas (दोषाः), dhatus and malas (मलाः) which are the building blocks of the body. Thus agni is an indispensable for Ayu (आयुः | life) of any individual. In the physical body, Agni is involved in the process of Paka (पाकः । Digestion and transformation). Different Ayurvedic texts mention that Agni is Pitta (पित्तम्), one of the tridoshas (त्रिदोषाणि) of the human body, which are vata (वातः), pitta (पित्तम्) and kapha (कफः).
The similarities between Agni in Ayurveda and Agni in other vedic literature
Agni (Samskrit: अग्निः) means Fire, Lighting, Purifier. According to vedas (वेदाः), it is the devata for fire, yajnas and divine knowledge. In vedavangamaya (वेदवाङ्मयम्), Agni has been praised in large number of mantras and suktas where it is considered to be the important devata next to Indra. Kindling of Agni, which generically refers to lighting of fire, is one of the important aspects in all वैदिकयज्ञः (Shrauta Yajnas or rituals prescribed in Vedas) and गह्ययज्ञः (Grhyayajnas, homas in domestic affairs such as that in samskaras). Agni carries the ahutis (oblations) of men to the devatas in heavenly worlds, who thereby pleased ensure the continuance of conditions favorable to mankind. Hence agni is considered to be the chief carrier of havishya (हविष्यम्) offered in Yajnas (यज्ञाः). Similarly Agni in body described in Ayurveda is the chief carrier of food from outside to the internal bodily elements in a processed form suitable and acceptable to them. Paka or Pachanam (the activity which includes acceptance of the offered food and its transformation into the substances similar to the body elements to make them available to body tissues as a raw material for their growth and repair) is believed to be the chief job of the Agni. Thus Agni is an important vital entity in Ayurveda. This does not limit the role of agni only up to the digestion of ingested food but also extends to absorption of substances through skin, accepting the sensory stimuli from sense organs and processing the information into the form suitable for one's life processes.
A unique feature about Agni in vedas is that it is classified and called by different names based on its purpose in yajnas (Shrauta | श्रौतः and smarta । स्मार्तः ), the ahutis (आहुति-s । oblations) offered and its use in laukika kriyas (cooking). Similarly Agni in Ayurveda has also been classified in different types based on its site and specific action.
Agni as one of the panchamahabhutas
Agni or tejas is one of the Panchamahabhutas (पञ्चमहाभूतानि the 5 basic elements in the nature).
- As a mahabhuta, rupa (illumination/vision) is the key attribute of Tejas or agni.
महाभूतानि खं वायुरग्निरापः क्षितिस्तथा| शब्दः स्पर्शश्च रूपं च रसो गन्धश्च तद्गुणाः||२७|| (Char. Samh. 1.27-29)
- Moreover, ushna (heat) is the characteristic feature to understand the presence of agni mahabhuta by touch (tactile perception).
खरद्रवचलोष्णत्वं भूजलानिलतेजसाम्| आकाशस्याप्रतीघातो दृष्टं लिङ्गं यथाक्रमम्||२९|| Char. Samh. 1.27-29)
What is Agni in Human body?
Ayurveda scholars have clearly mentioned that Agni resides in the Pitta which is one of the 3 doshas in the shariram (human body) . Thus the terms agni and pitta are used synonymously in Ayurveda shastra. Agni mahabhuta in the nature is responsible for generating light and heat. Similarly agni inside the body which is also called as Antaragni, does various jobs through the medium of pitta. Acharya Charaka has listed the various functions agni performs inside body as below,
अग्निरेव शरीरे पित्तान्तर्गतः कुपिताकुपितः शुभाशुभानि करोति; तद्यथा- पक्तिमपक्तिं दर्शनमदर्शनं मात्रामात्रत्वमूष्मणः प्रकृतिविकृतिवर्णौ शौर्यं भयं क्रोधं हर्षं मोहं प्रसादमित्येवमादीनि चापराणि द्वन्द्वानीति॥ (Char. Samh.12.11)
Meaning: It is the agni inside pitta in human body which performs various desirable and undesirable activities when it is in balanced state and vitiated state respectively viz. transformation and non-transformation, Vision and loss of vision, optimum or deranged level of heat, natural color or discoloration, bravery, fear, anger, delightfulness, delusions, graciousness etc and many more other pairs of opposites.
In the commentary on this sutra, acharya chakrapani has clarified that since the agni inside body is not morphologically similar to that present in nature which is in the form of flames, it is specifically mentioned that agni performs functions through the medium of pitta. Agni and pitta are inseparable. Various functions of agni or pitta described here are actually the specific functions of 5 types of pitta based on their location in the body. A type of pitta located at netra (eye) region in responsible for visual acuity in balanced state and loss of vision when vitiated. Similarly agni inside pitta located in jathara (stomach) is responsible for proper transformation or digestion. Agni inside pitta located in the twak (skin) controls the body temperature and the agni inside pitta located in Hrudayam controls various metal faculties like confidence, fear, anger etc. The skin color or complexion is also under the influence of agni inside pitta located in internal organs like yakrt and pliha.
Thus agni can be assessed on the basis of various visible aspects in one's body like color, digestion, strength, heat level, intelligence. 
Can agni exist in body without pitta?
Ayurveda acharyas have explained that agni inside the body can not exist without pitta. It can perform various actions only through the medium of pitta.
न खलु पित्तव्यतिरेकादन्योऽग्निरुपलभ्यते, आग्नेयत्वात् पित्ते दहनपचनादिष्वभिप्रवर्तमानेऽग्निवदुपचारः क्रियतेऽन्तरग्निरिति; क्षीणे ह्यग्निगुणे तत्समानद्रव्योपयोगात् , अतिवृद्धे शीतक्रियोपयोगात् , आगमाच्च पश्यामो न  खलु पित्तव्यतिरेकादन्योऽग्निरिति ||९|| Su su 21.9
Meaning: Agni can not exist without pitta. It is because of the agneyatwam (original nature of agni i.e. heat) of pitta which performs functions like burning, cooking/digesting (which are similar to agni in nature) it is treated like antaragni. If the agni nature of pitta reduces dravyas (substances) having similar nature to agni are utilized to kindle it, when this agni nature is excessively increased, cooling therapies are used to reduce its severity. Also we know it from the agama ( traditional doctrine or perspect also known as Shabda pramana or aptopadesha) that agni can not exist without pitta.
अग्निभेदाः॥ Types of the agni involved in food transformation
Agni inside the body is called by various different names at various instances. Although the agni or pitta is present everywhere and the same all over the body, it has been classified into various categories depending on its location and action specific to that location. Also agni inside substances that come in contact with our body when those are consumed has also been considered and has been given considerable attention.
Different texts mention different numbers of Agni present in the body, however according to the function and site of action there are 13 in number -
- 1 Jatharagni (जठराग्निः),
- 5 types of Bhutagnis (भूताग्नयः) and
- 7 types of Dhatvagnis (धात्वाग्नयः).
Jatharagni, the most important Agni, is present in Jathara (gut/gastrointestinal system) directly acts on four types of food, aids in digestion and transforms it into Rasa (रसः) and Mala (मलः । waste and toxins) thus, converting the gross matter to subtle substance thereby providing energy for body's needs. Thus it is called as the pachaka (transformer) of Annam or ahara. Since this being the first and foremost step in the transfer of energy in the form of food from outside to inside, without it no other agni can function and body can survive. Hence jatharagni is revered as Bhagawan or Ishwara (diety).
जाठरो भगवानग्निरीश्वरोऽन्नस्य पाचकः | सौक्ष्म्याद्रसानाददानो विवेक्तुं नैव शक्यते ||२७|| (Sush. Samh. 35.27)
जाठराग्नेः शरीरान्तरगतम् स्थानम्: ग्रहणी॥ Site of Jatharagni in body: Grahani
The site of jatharagni in the shariram (body) is known as Grahani. Grahani derives its name from its function to accept and hold food. Graha is the samskrit term which indicates to accept and hold. Grahani is located above nabhi (umbilicus) and is supported as well as maintained (in terms of the function) by the agni. It holds the undigested food, processes it and when completely processed that food matter is propelled further into the gut for further course of action. If this grahani is weak it fails to hold the food till its complete digestion and this undigested food known as aama is expeled out as it is.
अग्न्यधिष्ठानमन्नस्य ग्रहणाद्ग्रहणी मता| नाभेरुपर्यह्यग्निबलेनोपष्टब्धोपबृंहिता ||५६|| अपक्वं धारत्यन्नं पक्वं सृजति पार्श्वतः| दुर्बलाग्निबला दुष्टा त्वाममेव विमुञ्चति||५७|| (Char. Samh. 15.56-57)
पाकम् पाचनम् वा: जाठराग्नेः प्रधान कार्यम्॥ Pakam or pachanam : The chief function of Jatharagni
Digestion of the food and its transformation into Rasa dhatu is the chief funciton of jatharagni. There are multiple steps involved in the process of transformation wherein along with the jatharagni other doshas like kapha and vata also are involved and aid the function of agni. This has been described in depth in Ayurveda literature. The prana vayu is responsible for ingestion and swallowing of the food till its transfer from mouth to the amashaya (आमाशयः | initial part of the gut where the food is stored after coming through the food-pipe). In this part a type of kapha involved in food digestion helps in preparing the food for the process of digestion. By its gunas like drava and snigdha it makes the food soft and homogenous and propels further for digestion by agni. A type vata known as Samana vata kindles the digestive fire i.e jatharagni. When the ahara is taken on time and in proper quantity and quality it undergoes complete transformation in this way. The transformed food is separated into 2 parts namely Rasa dhatu and mala. Rasa dhatu then enters the circulation and provides nourishment to entire shariram mainly to dhatus. Ayurvedic scholars have explained this process of digestion and transformation with the help of a simple example of cooking rice in a pot kept on the flame of stove. The kapha plays role of water used in cooking, vata performs fucntion similar to lighting the stove or maintaining the flame and Agni is equated to the fire below the pot which actually cooks the rice.  
काले भुक्तं समं सम्यक् पचत्यायुर्विवृद्धये||७|| एवं रसमलायान्नमाशयस्थमधः स्थितः| पचत्यग्निर्यथा स्थाल्यामोदनायाम्बुतण्डुलम्||८|| Char. Samh. 15.5-8)
जाठराग्निभेदाः॥ Types of Jatharagni
The jatharagni has further been divided into 4 types based on its strength which in turn depends upon the predominant dosha affecting agni and the body overall. Dominance of Vata, Pitta, Kapha or the balanced state of all the 3 doshas lead to 4 different types of agni as listed below,
- Vishamagni (विषमाग्निः) - Due to Vata dominance. There is no constant intensity of the fire/ heat in this type which sometimes digests food faster and sometimes takes longer time to digest the same food.
- Teekshnagni (तीक्ष्णाग्निः) - It indicates very intense type of fire / heat inside the pitta. Hence with this type of agni the process of pakam (digestion) is very fast. Consequently the [erson feels hungry often and can digest even guru (heavy) ahara faster than the rest of the agni types.
- Mandagni (मन्दाग्निः) - Results due to the dominant kapha dosha. The intensity of this type of fire is very low leading to sluggish digestion process which causes blating of stomach, heaviness in stomach, dryness of mouth etc.
- Samagni (समाग्निः) - The balanced state of all doshas leads to the state of balanced agni of the body and it can further maintain the equilibrium of other body elements effectively.
It is known that, dhatus (the building blocks of body or tissues) acquire their nourishment from the ahara (food) that we ingest. different dhatus have different constitution of panchamahabhutas in them. Thus their nutritional requirements are distinct from with respect to the panchamahabhuta proportion in them. The bhutagni are present in each of the 5 mahabhutas and they perform the function of nourishing the similar mahabhuta present in body. Thus the function of nourishing or balancing the mahabhuta levels in the body is the chief function of bhutagnis present in the food.
Therefore, Ayurveda believes that ahara with similar properties (mahabhutas) can increase or nourish the body elements with similar properties (mahabhuta constitution) and vice versa. 
भौमाप्याग्नेयवायव्याः पञ्चोष्माणः सनाभसाः| पञ्चाहारगुणान्स्वान् स्वान् पार्थिवादीन् पचन्त्यनु॥ (Asht. Hrud. 3.59)
भूताग्निभेदाः॥ 5 Types of bhutagni
Types of bhutagni are based on the panchamahabhutas. Thus these types are
- Agni of Prthvi mahabhuta (पार्थिवग्नि/ भौमाग्नि)
- Agni of Jala mahabhuta (आप्याग्नि)
- Agni of Teja mahabhuta (तेजाग्नि/ आग्नेयाग्नि)
- Agni of Vayu mahabhuta (वायव्याग्नि)
- Agni of Akasha mahabhuta (नाभसाग्नि)
There are 7 dhatus with which the entire body is build up. All these dhatus derive their nutrition from the rasa dhatu formed at the end of digestion. Rasa Dhatu then undergoes further transformation at the level of each dhatu in order to provide the specific nutritional requirements of that dhatu and discard the unwanted or inadmissible portion called as dhatumalas (धातुमलाः) or malas (मलाः). At the same time, various upadhatus (उपधातवः) are also developed and nourished. Therefore dhatwagnis control the metabolic process at the dhatu level. It is also called as Sukshma-pachanam (सूक्ष्म पचनम्).
सप्तभिर्देहधातारो धातवो द्विविधं पुनः| यथास्वमग्निभिः पाकं यान्ति किट्टप्रसादवत् ॥ (Char. Samh. 15.15)
धात्वाग्निभेदाः॥ 7 Types of dhatvagnis
The human body is made up of 7 types of dhatus. Each of these 7 dhatus is generated, nourished and maintained by the agni of its own known as dhatvagni. It controls the dhatu level metabolism and levels of dhatus, upathatus dhatu malas etc. These 7 types of dhatvagnis are as follows,
- Rasa dhatvagni (रस धात्वाग्नि)
- Rakta dhatvagni (रक्त धात्वाग्नि)
- Mamsa dhatvagni (मांस धात्वाग्नि)
- Meda dhatvagni (मेद धात्वाग्नि)
- Asthi dhatvagni (अस्थि धात्वाग्नि)
- Majja dhatvagni (मज्जा धात्वाग्नि)
- Shukra dhatvagni (शुक्र धात्वाग्नि)
पञ्चपित्तभेदाः वा पञ्चाग्निभेदाः॥ 5 types of pitta or agni in body based on location
Apart from digestion and transformation of the food, agni inside pitta doshas performs various different functions. Thus 5 types of pitta doshas based on their chief site and peculiar function are also known as 5 types of agni performing different functions in the body.  These 5 types are,
- Pachaka pitta (पाचकपित्तम्) / Pachakagni (पाचकाग्नि)
- Ranjaka Pitta (रंजकपित्तम्) / Ranjakagni (रंजकाग्नि)
- Sadhaka Pitta (साधकपित्तम्) / Sadhakagni (साधकाग्नि)
- Alochaka pitta (आलोचकपित्तम्) / Alochakagni (आलोचकाग्नि)
- Bhrajaka pitta (भ्राजकपित्तम्) / Bhrajakagni (भ्राजकाग्नि)
The agni involved in the digestion, absorption, assimilation of food leading to formation of doshas, rasa dhatu and malas of food like purisha (stools), mutram (urine) in known as pachakagni. It is the chief agni which also provides strength and controls function of all other types of agnis involved in various different functions in the body. It is located in the koshtha (roughly equivalent to gut) between Pakwashaya (roughly equivalent to large intestine) and Amashaya (roughly equivalent to stomach). 
Ranjaka means coloring agent. Agni that is present in pitta located at Yakrt (roughly equivalent to liver) and Pleeha (roughly equivalent to speen) acts on Rasa dhatu to help it transform into rakta dhatu by adding color pigments to it is known as ranjakagni. 
Sadhaka means fulfilling or accomplishing agent. The agni located inside pitta present in the Hrdayam (the vital organ associated with mind, senses, intelligence, life energy etc) in palys indispensible role by becoming the effective agent to accomplish what is desired by the individual. Thus it is known as sadhakagni. 
The agni inside pitta located in the sensory visual organ or eye which can capture the outside images and generate the appropriate signals for visual perception is known as alochakagni.
The agni inside pitta located in twak (skin) is called as bhrajakagni. It can absorb the externally applied substances like oil, medicate liquids, packs etc on skin and make them available to body tissues. Since it is also the factor responsible for appearance of chaya (Chaya means shadow or shade or skin complexion. It is generally indicate changes in complexion due to a disease pathology.) on one's body/skin it is called as bhrajaka (bhraj- lusture/shine) agni.  Chhaya has been deeply studied in Ayurveda. It is believed to be associated with the imbalances in the internal bodily environment and thus any change in the body inside can be reflected outside through chhaya which can affect the original color and complexion of the individual. Since the agni inside skin has the potential to reflect / throw light on / illuminate the changes in internal environment of body through chaya of skin (which can be visible outside) it is calle das illuminator/ reflector i.e. bhrajakagni.
Relation between all agni types
In all the types of agni mentioned above the one which digests ahara (food) i.e. Jatharagni is believed to be the chief. Maintenance of strength or status of all the other types of agni is dependent upon the jatharagni. If jatharagni is strong and stable sp would be the other types of agni and vice versa. Thus acharyas emphasize on keenly take care of jatharagni by offering it only the vidhivat ahara (see : Healthy food habits) because the status of ayu (life) and balam (strength and immunity) is rooted in this agni.
अन्नस्य पक्ता सर्वेषां पक्तॄणामधिको मतः| तन्मूलास्ते हि तद्वृद्धिक्षयवृद्धिक्षयात्मकाः||७१|| तस्मात्तं विधिवद्युक्तैरन्नपानेन्धनैर्हितैः| पालयेत्प्रयतस्तस्य स्थितौ ह्यायुर्बलस्थितिः||७२|| (Asht. Hrud. 3.71-72)
देहे अग्निकार्याणि॥ Role of agni in human physiology according to ayurveda
Agni is an integral part of human body mechanics. In order to survive in the nature every individual has to establish a relationship with the nature. Through this relationship one's internal and external environment maintain a harmony and purusha can survive and grow in the loka (external world/nature) as a part of it. However, this can be achieved only when one can take up the substances from outer world and convert them in a form suitable for acceptance by the body tissues so that it can be made use of to grow and repair the internal bodily environment. At the same time, the wastes generated through this process which are not compatible for body are separated by the agni and thrown out of the body. Thus agni plays the vital role of establishing and maintaining this crucial link between the man and the world. This function happens at multiple levels and thus the agni plays key role in maintenance of health and well-being. These various aspects of health controlled that are under the control of agni are listed by all the Ayurveda acharyas and thus they call agni the root of not just body but life.
- Charaka Samhita praises agni and describes its role in health, wellness, illness, life and death.
आयुर्वर्णो बलं स्वास्थ्यमुत्साहोपचयौ प्रभा| ओजस्तेजोऽग्नयः प्राणाश्चोक्ता देहाग्निहेतुकाः||३|| शान्तेऽग्नौ म्रियते, युक्ते चिरं जीवत्यनामयः| रोगी स्याद्विकृते, मूलमग्निस्तस्मान्निरुच्यते||४|| (Char. Samh. 15.3-4) Meaning: Dehagni (all the entities in the body that are responsible for digestion and metabolism) is the fundamental causative agent for longevity, normal complexion, normal strength, good health, motivation, normal growth, normal luster, normal ojas, normal body temperature and various other forms of agni. Even the existence of an individual is said to be because of dehagni. When the agni stops functioning, the individual dies; if the agni functions normally, the individual can lead a healthy and long life. Similarly, if the agni becomes abnormal, the individual suffers from various diseases; and hence, the agni is said to be the root cause of health and longevity. 
- Acharya Vagbhata in his treatise Ashtanga Hrdayam has delivered the similar message,
तच्चान्नं विपक्वमेव देहधात्वादिपोषणम्, नापक्वम्| तस्य चान्नपाकस्य हेतुरग्निः, अत आह----
तत्राग्निर्हेतुराहारान्न ह्यपक्वाद्रसादयः||५४|| (Asht. Hrud. 3.54)
Meaning: Only the completely digested (and transformed) food provides nutrition to dhatus (body tissues) and not the undigested/unmetabolised (untransformed) food. This digestion and metabolism can occur only by the agni therefore it is believed that, the food that nourishes dhatus, ojas, balam (strength) , varna (complexion) etc can help due to the agni (which acts on it and transforms it). This nourishment can not occur at all through the undigested food stuff.
- Other functions of agni in body
Along with the main function of paka / pachana of food, agni is helpful in relieving aama (undigested food material of toxic nature), stiffness, cold or hypothermia, aches & pains, cramps etc in the body.
अग्निरामस्तम्भशीतशूलोद्वेपनप्रशमनानां (Char Samh 25.40) Meaning: Agni is the prime agent in reducing aama, stiffness, cold, pains and aches etc.
स्नेहस्य अग्निवृद्धिकरत्वम्॥ Role of sneha in agni strength
Effect of sneha (unctous substances / certain fatty substances) on the agni is well-known to everyone. We know that when we add oil or ghee like substances which are snigdha (unctuous in property) onto the burning fire the flame immediately increases. Ayurveda acharya have explained that the same is applicable to the agni inside the body. As strong firewood greased with oil or any unctuous substance on coming in contact with the agni increases or becomes strong, food that has some unctuousness substance in it ignites the agni inside the body. Thus it is always recommended to food topped with ghee in Bharateeya Samskrti and Ayurveda.
दीप्तो यथैव स्थाणुश्च बाह्योऽग्निः सारदारुभिः| सस्नेहैर्जायते तद्वदाहारैः कोष्ठगोऽनलः||७९|| (Asht. Hrud. Adhyaya Sutra 79 )
आहारमात्रा तथा अग्निः संबन्धः॥ Role of quantity of food in agni strength
Ahara or Food is the fuel for the agni. Thus the strength of the agni primarily depends upon the quantity of the food. Ayurveda scholars therefore have pointed out that the best way to kindle the agn is to feed it with the right amount of ahara (food) . Right amount is different for each and every individual and that depends upon the natural strength of that individual's agni from his birth. If some person has teekshna (strong) agni then it might require more food to maintain its strength than other persons manda (sluggish) agni which would be maintained with very less amount of food.
यथाग्न्यभ्यवहारोऽग्निसन्धुक्षणानां (Char. Samh. 25.40)
Agni: savior or killer
Agni has a power to nourish and maintain the life when it is fueled with the right amount and quality of the ahara. But when this agni is not properly taken care of it also possess the capacity to even end the life. The exact stepwise process and the logical reasoning behind it has been clearly mentioned in Ashtanga Hrudayam of Acharya Vagbhata.
आहारमग्निः पचति दोषानाहारवर्जितः| धातून् क्षीणेशु दोषेषु जीवितं ढातुसङ्क्षये||९१|| (Asht. Hrud. 10.91) Meaning: Agni digests food. When food the unavailable it digests doshas, when the doshas have reduced and unavailable to agni then it reaches to dhatus and starts digesting those. At last when even dhatus are unavailable it ends life (liberates prana).
This sutra holds significant importance in the field of Ayurveda chikitsa. Keeping this fact in mind a vaidya can make make use of one's agni for treating his diseases and also to find causative factors for disease developments. Thus one must take utmost care of this powerful fire element i.e. agni in body so as to achieve complete health and well-being.
अग्निदुष्टिहेतवः॥ Causes of disturbances in Agni
There are multiple factors in diet and lifestyle of an individual which directly affect the agni and later its strength, affect its function. One must know these factors in order to prevent disturbances in agni and all the resultant body functions. The common factors are listed below,
- Abhojana (अभोजनात्) - Starving
- Ajirabhoajana (अजीर्णभोजनात्) - Eating frequently at short intervals before the previous food is digested and stomach is light
- Atibhojana (अतिभोजन) - Overeating
- Vishamashana (विषमाशनात्) - Not following the fixed timing for meals (irregularity in food intake)
- Asatmya ahara, guru ahara, shita ahara, ruksha ahara and dushta ahara sevana (असात्म्यगुरुशीतातिरूक्षसन्दुष्टभोजनात्)- Eating incompatible, heavy to digest, cold, dry and spoiled food
- Virechana vibhrama, vamana vibhrama, sneha vibhrama (विरेकवमनस्नेहविभ्रमात्) - Improper execution of panchakarmas like virechana, vamana and snehana
- Vyadhi karhsana (व्याधिकर्षणात्) - Due to prolonged illness or chronic diseases
- Desha vaishamya, kala vaishamya, rutu vaishamya (देशकालर्तुवैषम्यात्) - Change in place, time and season
- Vega vidharana (वेगानां च विधारणात्) - Suppressing the natural urges called as vegas
Thus it is highly recommended to be cautious to avoid or control these factors in one's lifestyle so as to guard one's agni. Once this agni is vitiated it can not perform its basic function well. It then can not even digest even the light food properly. In such cases whatever the food is ingested it is improperly processed and becomes fermented which subsequently becomes toxic in nature.
दुष्यत्यग्निः, स दुष्टोऽन्नं न तत् पचति लघ्वपि| अपच्यमानं शुक्तत्वं यात्यन्नं विषरूपताम्॥ (Char. Samh. 15.44)
अग्निपरिक्षा॥ How to examine agni?
Agni, the fire element inside humans is not seen separately but it is present inside the pitta dosha. May it be th eagni or pitta dosha, both these are just the biological forces present inside us. Though they have physical dimension to them one can not see them or check them with the help of naked eyes or even any lab test. However, agni or pitta being so vital for one's existence, even inancient times ayurveda scholars found it necessary to assess those for diagnosis and treatment of diseases. Therefore Ayurveda samhitas provide method to examine the agni inside one's body and that method is by prashna pariksha i.e. by interrogation. 
- Charaka Samhita (Sharirasthanam Adhyaya 1 Sutra 27-29)
- Charaka Samhita (Sutrasthanam Adhyaya 12 Sutra 11)
- Charaka Samhita (Sutrasthanam Adhyaya 15 Sutra 4)
- Sushruta Samhita (Sutrasthanam Adhyaya 35 Sutra 27)
- Charaka Samhita (Chikitsasthanam Adhyaya 15 Sutra 56-57)
- Charaka Samhita (Chikitsasthanam Adhyaya 15 Sutra 5-8)
- Ashtanga Hrdayam (Sharirasthanam Adhyaya 5 Sutra 36)
- Charaka Samhita (Chikitsasthanam Adhyaya 15 Sutras 74-77)
- Charaka Samhita (Chikitsasthanam Adhyaya 15 Sutra 60)
- Ashtang Hrudaya (Sharirasthanam Adhyaya 3 Sutra 59)
- Charaka Samhita (Chikitsasthanam Adhyaya 15 Sutra 15)
- Sushruta Samhita (Sutrasthanam Adhyaya 21 Sutra 10)
- Charaka Samhita (Indriyasthanam Adhyaya 7 Sutra 10-17)
- Ashtanga Hrudayam (Sharirasthanam Adhyaya 3 Sutra 71-72)
- Charaka Samhita (Chiktisasthanam Adhyaya 15 Sutra 3-4)
- Available from charakasamhitaonline.com
- Ashtanga Hrudayam (Sharirasthanam Adhyaya 3 Sutra 54)
- Charaka Samhita (Sutrasthanam Adhyaya 25 Sutra 40)
- Ashtanga Hrudayam (Chikitsasthanam Adhyaya Sutra 79 )
- Charaka Samhita (Sutrasthanam Adhyaya 25 Sutra 40)
- Ashtanga Hrudayam (Chikistasthanam Adhyaya 10 Sutra 91)
- Charaka Samhita (Chikitsasthanam Adhyaya 15 Sutra 42-45)
- Sushruta Samhita (Sutrasthanam Adhyaya 10 Sutra 5)