In Traditional Chinese Medicine (TCM), Bai Jie Zi belongs to the 'Cool herbs that transform Phlegm and stop Cough' category. In TCM Phlegm is a condition of Stagnation of Fluids which tends to start in the Spleen and then goes to the Lungs. If this overly accumulates it thickens and becomes pathological Phlegm. Phlegm, being a form of Stagnation, often starts as being Cool and transforms to Hot as the condition progresses. The herbs in this category are Cold in nature so they treat the later stages of the Stagnation: Hot and Dry-Phlegm with symptoms such as cough, goiter or scrofula.
As suggested by its category Bai Jie Zi is Warm in nature. This means that Bai Jie Zi tends to help people who have too much 'Cold' in their body, although with less effect than a plant that would be Hot in nature. Balance between Yin and Yang is a key health concept in TCM. Those who have too much Cold in their body are said to either have a Yin Excess (because Yin is Cold in nature) or a Yang Deficiency (Yang is Hot in Nature). Depending on your condition Bai Jie Zi can help restore a harmonious balance between Yin and Yang.
Bai Jie Zi also tastes Bitter. The so-called 'Five Phases' theory in Chinese Medicine states that the taste of TCM ingredients is a key determinant of their action in the body. Bitter ingredients like Bai Jie Zi tends to have a cleansing action on the body by clearing Heat, drying Dampness and promoting elimination via urination or bowel movements.
The tastes of ingredients in TCM also determine what Organs and Meridians they target. As such Bai Jie Zi is thought to target the Stomach and the Lung. In TCM the Stomach is responsible for receiving and ripening ingested food and fluids. It is also tasked with descending the digested elements downwards to the Small Intestine. In addition to performing respiration, the Lungs are thought in TCM to be a key part of the production chain for Qi and the Body Fluids that nourish the body.