Clear Heat / Dry Damp: Huang Bai

Huang Bai= "Yellow fir" It is the bark of the Chinese cork tree:

Huang Bai goes to the Kidney and Bladder. It is bitter and cold. This tells us a lot--it drains damp heat from the lower burner. What does damp heat look like in the lower burner? Yucky, that's what: thick, yellow vaginal discharge; foul-smelling diarrhea; dysentery. Ew. It can also move downward into the legs causing red, swollen, painful knees, legs, or feet. It's also for damp heat jaundice (the bright yellow kind).

Then there's thing called kidney fire, which has nothing to do with chili. Huang Bai will cool down the kidneys if the yin has burned out and the yang fire is raging causing "steaming bones," night sweats, afternoon fevers/sweating, and nocturnal emissions. It is important to note that while it clears this kidney fire, it does not actually nourish the kidney yin.
Huang Bai will drain toxic fire generally as well, the sort that causes sores and damp lesions.

I like Bensky's commentary where he says that Huang Bai "controls clumped heat in the organs, stomach and intestines...."