In the theory of Tibetan medicine, why are all skin problems collectively referred to?

According to Tibet Sunshine official website, in Tibetan medicine theory, all skin problems are collectively referred to as yellow water.

Tibetan doctors believe that the occurrence of skin diseases is closely related to wind, evil and poison. Among them, ethos and pathogens refer to various external pathogenic factors, including physical and chemical stimuli, pathogenic microorganisms such as bacteria and viruses, allergens and so on. These external factors directly harm the skin and are the external conditions for the occurrence of skin diseases. Toxic gas is the general name of pathogenic factors in the body, which is caused by the imbalance of metabolism and immune function in the body and is the internal cause and fundamental factor of skin diseases.