Jing

Chinese medical theory holds that jing, qi and shen form the Three Treasures, sanbao, a hierarchy of increasingly refined substance and function, with jing as the densest and most foundational of the three. Prenatal jing, xiantian zhi jing, is inherited once, at conception, from the combined essence of one's parents, is fixed in total quantity, and is slowly spent over the course of a lifetime; postnatal jing, houtian zhi jing, is continually extracted from food and air and can replenish the system day to day, though it cannot restore what prenatal jing has lost.

Both are stored chiefly in the kidneys, which the Huangdi Neijing and later texts treat as the root organ of growth, reproduction, bone and marrow, and hearing, so that kidney-jing deficiency is diagnosed behind conditions of infertility, weak bones, premature graying and developmental delay in children. Daoist internal alchemy, neidan, builds its entire practice on this hierarchy, describing cultivation as a three-stage refinement: jing is refined into qi, qi is refined into shen, and shen is finally returned to emptiness or the Dao, a sequence that makes conserving jing, especially through moderating sexual activity, the necessary first step before the higher refinements can proceed.

Jing is regularly translated as "essence" in English-language Chinese medicine texts, a rendering that is broadly accurate but flattens the term's association with reproductive fluid specifically, a connection stronger and more literal in the Chinese than "essence" alone suggests to an English reader; some translators use "vital essence" or "reproductive essence" to preserve that link. Giovanni Maciocia's widely used clinical textbook The Foundations of Chinese Medicine is among the standard modern routes by which practitioners outside China learn the jing-qi-shen framework in detail.

The idea that jing is finite and depleted by sexual activity has made semen-retention and related conservation practices a recurring feature of both historical Daoist sexual alchemy and its modern popular offshoots, some of which extend the classical medical claim well beyond what the Huangdi Neijing itself asserts. As with qi, jing belongs to a living medical and religious tradition rather than to a claim that has been put to controlled experimental test, and it is described here in its own clinical and alchemical terms rather than measured against a standard the tradition never proposed to meet.