Keep your instrument free from perspiration. Wipe the perspiration from your horn. Using a leather valve protector can be helpful but replace the protector periodically because perspiration soaks into and through the material. Saliva from the mouth also contains acids, which attack metal. Carbonic acid is present at all times in saliva and other acids are formed in the mouth, depending on food eaten and hygienic conditions of the mouth.
Soft solder is especially subject to the effects of saliva acids.
Water key nipples, which are soft soldered, can be eaten out entirely. That is why the inside of instruments must be cleaned often and thoroughly. It is assumed that the reader will recognize the need to avoid kissing or drooling on their favorite instrument no matter how high a note they hit. After using the instrument, be sure all saliva and water are wiped off the instrument before putting it away. But whatever you call it, it is filth that you should get rid of.