Ojas and health as per Ayurveda's principles...

The health of the immune system determines whether diseases or warded off. Ayurveda notes that there is a sap-like material called Ojas (perhaps analogous to pineal gland secretion) that coats the immune system and protects it from diseases. If the Agni fire is too low or too high, this life sap will be diminished. Just like the tree that creates a sap over the bruise in the bark to protect and heal the bruise, our life sap (Ojas) protects and heal us from illness.

[Ojas]

Too much dryness or too much heat and fire eat away the life sap. A weak immune system is the cause of the illness, from cold to multiple sclerosis to AIDS. To heal the immune system, one needs adequate rest and pure (sattvic) foods and herbs that specifically rebuild the Ojas (life-sap). (Here a point should be noted very clearly that non-vegetarian food never rebuilds the immune, it is just for the taste and many doctors prescribing non-vegetarian soups and food is just for fancy a placebo working for Psychological satisfaction; our body is not equipped to eat non-veg but our body structure externally and internally made suitable for pure vegetarian food only).  Some of the examples of Oja's building herbs are Satavari roots (Asparagus racemosus) and ashwagandha roots (Withania somnifera).

Maintaining our body's immune system is very easy but need a proper and balanced diet as well as a minimum of 6-8 hrs proper body rest (No daytime sleeping). If we maintain Ojas and doshas in our body, we will be free from any disease as we know that any disease can be caused by any of the humor, depending on which sites, they relocate to, so, the patient is examined completely, using all possible methods. Since, disease development (pathogenesis) is the same for all dosha only the humor, stages, sites, and directional movement of the humor are examined. (Humor have to return to their origin sites to be eliminated).

So, we can say Ayurveda emphasizes promoting health, preventing disease, and enhancing longevity (rejuvenation and age reversal). By using Rasayana (rejuvenation) promoting herbs and diet, good conduct, daily routine, and seasonal living longevity are developed.

Stay healthy, stay safe...