Rasa Dhatu (रस धातु)
The Samskrit word 'Rasa' (रसः) has various meanings like extract/juice, taste, interest and even mercury. However in the context of human body, the word 'Rasa' used in Ayurveda refers to a body tissue or body component which is the first among 7 dhatus (धातु) described in Ayurveda. This body tissue is in the fluid form. It is formed after digestion of food as an extract of food and helps to nourish the body. It is also called as 'Ahara-rasa' (आहार-रसः) i.e. extract of food in liquid state. It performs the function of nourishing the physical body.
निरुक्तिः ॥ Etymology
Sushruta Samhita has given nirukti of the word 'rasa' as follows,
तत्र ‘रस’ गतौ धातुः, अहरहर्गच्छतीत्यतो रसः ॥ (Sush. Samh. 14.13)
tatra ‘rasa' gatau dhātuḥ, aharahargacchatītyato rasaḥ ॥ (Sush. Samh. 14.13)
Meaning: The term Rasa is derived from the root ‘gatau’ (गतौ) and it means flow or movement. Since this dhatu constantly keeps on circulating day and night in our body to provide nourishment to body tissues, it is known as rasa.
रसधातुउत्पत्ति:॥ Formation of rasa dhatu
Rasa dhatu is formed from food. We consume various type of foods which are either chewed, swallowed, drank or licked. Food in any such form undergoes the process of transformation by Agni in the stomach. Agni performs the function of digestion of this food and then that food taken from outside is transformed into a form that is acceptable by the body, so that body can utilize that for replenishment. Body can accept the food to fulfill energy demands, only if this food is available in a specific form. If the extract of the food is not in this specific form, it is called as 'Aama' (आमः) which acts like a foreign body or toxin. It can not be utilized for growth and development rather it initiates the process of development of various diseases. Thus it is highly important that, the food that a person eats, undergoes proper digestion and fluid extract of a specific form is obtained from it. Only such a food extract ultimately reaches body tissues, provides nourishment to them and called as Rasa dhatu according to Ayurveda.
रसधातोः पांचभौतिकत्वम् ॥ Panchabhoutik constitution
Rasa dhatu is obtained from food which is mostly solid or liquid. After transformation the rasa dhatu that is formed is obtained in a fluid form. Thus Prthvi (पृथ्वी | earth) and Jala (जलम् | water) element are dominant in Rasa dhatu.
रसधातोः स्थानम् ॥ Location of Rasa dhatu
Rasa dhatu circulates through channels and a network system known as Rasavaha srotas (रसवह स्रोतस). However it is mainly located in Hrudayam (हृदयम्) which is also the chief site of Manas (मनः) and Prana (प्राणः). From this site, Rasa dhatu is distributed all over the body through various dhamanis (धमन्यः | vessels).
रसधातोः कार्यम् ॥ Function
Rasa dhatu is formed as as extract of food. And thus, it acts as a food for rest of the body tissues. Nourishment is the main function performed by it. Various function performed by rasa dhatu are listed below,
- Prinana (प्रीणनम्) / Tarpana (तर्पणम्): Nourishment of the whole body
- Vardhana (वर्धनम्): growth and development of body tissues
- Satiety (तुष्टिः) : Rasa dhatu is responsible for and associated with the feeling of satiety which is physical as well as a psychological aspect of a human being.
- Nourishing Rakta dhatu (रक्तपुष्टिः) : Part of Rasa dhatu undergoes further transformation to generate rakta dhatu and nourish the existing one.
रसधातोः उपधातवः॥ Upadhatu of Rasa dhatu and their function
Rasa dhatu when subjected to the process of micro-transformation (सूक्ष्मपचनम्), it generates 2 more entities which are known as Upadhatus (उपधातु) of Rasa dhatu. Ayurveda Acharya have opined that Raja (रजः) or Artavam (आर्तवम्) equivalent to menstrum and ovum is one upadhatu of rasa dhatu. Stanya (स्तन्यम्) i.e. breast milk of a lactating woman is the second upadhatu of Rasa. 
रसधातोः मलम् ॥ Mala of Rasa dhatu
During the micro-transformation of Rasa dhatu inside body and formation of upadhatus, some fluid secretion is generated as a waste byproduct and it is called as ‘kapha’ (कफः). However, this is waste or unwanted kapha which resembles Kapha dosha. Thus, Kapha dosha is closely associated with rasa dhatu. The clinical features of increase in rasa levels of body are similar to those of kapha dosha increase.
रसधातोः स्रोतसम् ॥ Site of metabolism and Channel of transport
Rasa dhatu undergoes metabolic transformation in the network system or channel known as Rasavaha srotas. Mahasrotas (महास्रोतसम् | similar to gastrointestinal tract) and hridayam (हृदयम्) are the 2 chief organs of Rasavaha srotas. Rasa dhatu is formed in Mahasrotas and then reaches upto hrudayam.
रसधातुदुष्टिहेतवः ॥ Vitiating factors
Rasa dhatu is formed after proper digestion of food. Thus the dietary factors and also some lifestyle related factors directly affect rasa dhatus formation and function. These factors set out the background for development of various diseases which involve rasa dhatu e.g jwara (ज्वरः). Few such factors that directly vitiate rasa dhatu are listed below.  and its function are listed as below.
- Repeated intake of heavy to digest food (गुरुआहार)
- Intake of food or drinks that are very cold (अतिशीत सेवनम्)
- Intake of food that has excess fat content (अतिस्निग्ध सेवनम्)
- Overeating (अतिमात्रं समश्नताम्)
- excessive mental stress and over thinking (चिन्त्यानाम् अतिचिंतनात्)
रससारलक्षणानि ॥ Characteristics of person having supreme quality rasa dhatu
Those who have supreme quality of rasa dhatu in a body are identified by some characteristic features. These features are called as rasa-sarata features (रससारता लक्षणानि). Most of these features are manifested on skin and therefore this is also called as Twaksarata (त्वक्सारता). Thus one can identify the quality of rasa dhatu by assessing presence or absence of following signs in skin.
तत्रस्निग्धश्लक्ष्णमृदुप्रसन्नसूक्ष्माल्पगम्भीरसुकुमारलोमासप्रभेवचत्वक्त्वक्साराणाम्| सासारतासुखसौभाग्यैश्वर्योपभोगबुद्धिविद्यारोग्यप्रहर्षणान्यायुष्यत्वंचाचष्टे ॥ (Char. Samh. 8.103)
tatrasnigdhaślakṣṇamr̥duprasannasūkṣmālpagambhīrasukumāralomāsaprabhevacatvaktvaksārāṇām| sāsāratāsukhasaubhāgyaiśvaryopabhogabuddhividyārogyapraharṣaṇānyāyuṣyatvaṁcācaṣṭe ॥ (Char. Samh. 8.103)
Meaning: In persons who are tvaksara (having constitutional essence of skin), the skin is unctuous (snigdha), smooth (shlakshna), soft (mridu), clean and fresh/adorable (prasanna) with fine (sukshma), thin (alpa), deep rooted (gambhira) and delicate (sukumara) hairs and is lustrous (prabha). This essence indicates happiness, good fortune, power, enjoyment, intelligence, knowledge, health, cheerfulness and longevity.
In this way various physical, psychological, emotional and social aspects of having superior quality of rasa dhatu are mentioned by Ayurveda acharyas.
रसस्य प्रधानता ॥ Importance of Rasa dhatu in health and wellbeing
Rasa dhatu is that body fluid which provides nourishment to the body. Thus growth, development and nourishment of rest of the body tissues is totally dependent on rasa. Thus, it plays pivotal role in maintaining one's life. Therefore it is said that purusha develops from rasa as described by Acharya Sushruta in the following sutra,
रसजं पुरुषं विद्याद्रसं रक्षेत् प्रयत्नतः | अन्नात्पानाञ्च मतिमानाचाराञ्चाप्यतन्द्रितः ॥ (Sush, Samh. 14.12)
rasajaṁ puruṣaṁ vidyādrasaṁ rakṣet prayatnataḥ | annātpānāñca matimānācārāñcāpyatandritaḥ ॥ (Sush, Samh. 14.12)
Meaning: The existence of purusha depends upon rasa. Therefore, one should protect and maintain the quality and quantity of rasa dhatu with utmost care. It can be achieved through proper diet and lifestyle. Since the whole body receives nourishment and energy through rasa, if the body has to be kept healthy and strong, one needs to take utmost care of rasa dhatu. One of the 8 branches of Ayurveda known as 'Rasayana' deals with revitalisation and rejuvenation therapies. These also enhance one's immunity and slows down the process of degeneration or ageing. In order to achieve this, Rasa dhatu should be balanced and enhanced. Thus, this branch of Ayurveda has been named after the Rasa dhatu and called as 'Rasayana Chikitsa' (रसायन चिकित्सा). It helps in maintaining the best qualities of rasa dhatu and other body components.
रसायनतन्त्रं नाम वयःस्थापनमायुर्मेधाबलकरं रोगापहरणसमर्थं च । (Sush. Samh. 1.7)
rasāyanatantraṁ nāma vayaḥsthāpanamāyurmedhābalakaraṁ rogāpaharaṇasamarthaṁ ca ।
Meaning: Rasayana as a measure, which prolongs and provides positive health. improves mental faculties and provides resistance and immunity against diseases.
- Sushruta Samhita (Sutrasthanam Adhyaya 14 Sutra 13)
- Dwarkanath C. Introduction to Kayachikitsa. Chaukhambha Orientalia. Varanasi; 1996. Third edition.pg.320
- Sushruta Samhita (Sutrasthanam Adhyaya 14 Sutra 3)
- Ashtanga Hrudayam (Sutrasthanam Adhyaya 11 Sutra 4)
- Sushruta Samhita (Sutrasthanam Adhyaya 15 Sutra 5)
- Charaka SAmhita (Chikitsasthanam Adhyaya 15 Sutra 17)
- Charaka Samhita (chikitsasthanam Adhyaya 15 Sutra 18-20)
- Charaka Samhita (Vimanasthanam Adhyaya 5 Sutram 13)
- Charaka Samhita (Vimanasthanam Adhyaya 8 Sutra 103)
- Available From Charaksamhitaonline.com
- Sushruta Samhita (Sutrasthanam Adhyaya 14 Sutra 12)
- Sushruta Samhita (Sutrasthanam Adhyaya 1 Sutram 7)