Phlegm has a great importance in Chinese Medicine as it is both a condition in and of itself as well as a cause for other diseases.

The main cause for the formation of Phlegm is Spleen Deficiency since the Spleen rules the transformation and transportation of Body Fluids. If this function is impaired, Body Fluids accumulates and change into Phlegm.

The Lungs and Kidneys may also be involved since they each play a role in handling body Fluids: the Lungs disperse and descend Body Fluids while the Kidneys transform and excrete them. Again, if they fail to perform those roles, Body Fluids will accumulate and become Phlegm.

That being said, the Spleen malfunction is the fundamental reason behind the formation of Phlegm and, as such, treatments will focus on it first and foremost.

There are two broad types of Phlegm: so-called "Substantial Phlegm" and "Non-Substantial Phlegm". Simply put, Substantial Phlegm can be seen, such as sputum in the Lungs and throat. Non-Substantial Phlegm is more hidden and will manifest itself into, for instance, kidney stones, gallstones or arthritic bone deformities.

Phlegm can accumulate and settle down in different parts of the body and lead to corresponding symptoms. For example, if it stays in the joints, muscles and Channels, there are muscle numbness, bone deformities and etc. If it mists the Heart, it causes many mental illness. If it settles in the Gall Bladder or Kidney, it leads to stones in these Organs.

Phlegm can further be categorized according to its nature: there is Damp-Phlegm, Phlegm-Heat, Cold-Phlegm, Wind-Phlegm, Qi-Phlegm, Phlegm-Fluids and etc.

"Phlegm-Fluids" is very similar to Dampness and is very watery and thin. It can be heard splashing in the body, found usually in the Stomach and Small Intestines, hypochondrium, limbs or above the diaphragm.