Yin Deficiency involves the excessive consumption of Body Fluids, Essence and Blood. The main cause is overwork, which usually develops very gradually and slowly over several years. The only exception to a rapid Yin Deficiency is when Pathological Heat consumes Body Fluids and Yin very fast.

If Yin Deficiency persists for a long time, like many years, it eventually leads to the development of Interior Heat of an Empty nature. The Heat occurs due to lack of Yin rather than Yang Excess, which is the precursor of Full-Heat. Both patterns have Heat features, but in different way. The Full-Heat manifestation exists all the time and is easy to be seem. The Empty-Heat's symptoms are comparatively less strong, like body heat but mostly in palms and soles, mild feeling of heat but only in the afternoon or evening, a dry mouth and desire to drink but only in small sips, red face but only malar flush, fever but only low-grade in the afternoon.

As for mental related symptoms, Empty-Heat just causes some mild restlessness which gets worse in the afternoon or evening. However, Full-Heat gives rise to severe mental restlessness, agitation, anxiety, insomnia with agitated sleep. Full-Heat happens more for acute diseases while Empty type is more chronic. Also, Empty-Heat is more comment among women, especially the elderly or these with weak constitution.

Please be aware that Empty-Heat does not necessarily always happen with Yin Deficiency. Tongue color is also an important indicator. Yin Deficiency manifests on the tongue with a lack of coating. A tongue without coating but of a normal colour reflects Yin Deficiency (without Empty-Heat). A red tongue without coating indicates Yin Deficiency with Empty-Heat.