Taixi (胎息, "embryonic breathing" or "embryonic respiration") refers to Daoist meditation and neidan Inner Alchemy methods, the principle of which is to breathe like an embryo or fetus in the womb, without using nose or mouth. Techniques developed for embryonic breathing include xingqi (行氣, "circulating breath"), biqi (閉氣, "breath retention; apnea"), fuqi (服氣, "ingesting breath; aerophagia"), and taishi (胎食, "embryonic eating; swallowing saliva").
In the history of Daoism, Tang dynasty (618-907) Daoist Internal Alchemists fundamentally changed the nature and understanding of embryonic breathing from the ancient theory of waiqi (外氣, "external qi of the air; external breathing") to the new theory of neiqi (內氣, "internal qi of one's organs; internal breathing"). Instead of inhaling and retaining waiqi air, adepts would circulate and remold visceral neiqi energy, which was believed to recreate the yuanqi (元氣, "prenatal qi; primary vitality") received at birth and gradually depleted during human life. Taixi (胎息, "embryonic breathing") was associated with the shengtai (聖胎, "sacred embryo; embryo of sainthood"), which was originally a Chinese Buddhist concept that Tang Daoists developed into a complex process of symbolic pregnancy giving birth to a spiritually perfected doppelganger of oneself.
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