Dezincification or "Red Rot"
Dezincification is a form of corrosion and weakening of brass instruments in which zinc is dissolved from the brass alloy. What causes this to occur? Spit sitting inside of the instrument. Human spit is acid in order to help breakdown food in our mouths. Everyone's biology is a little different so some people have more acidic spit than others. The process is internal, its very easy to not even know that dezincification has occurred. The acid essentially "eats" its way through the brass and eventually becomes visible with its tell tale pink or red coloring, thus the term "Red Rot." Its easier to see the damage on yellow brass instruments compared to silver because of the stark contrast in color.
Silver plated brass instruments are just that, silver plated. Underneath the silver is brass. As the "Red Rot" progresses, flakes of silver can be seen coming off of the instrument. All brass instruments are susceptible to dezincification and the potential for structural failure. As "Red Rot" progresses the metal will become weaker and weaker until little pin sized holes appear and then the instrument has air leaking which can affect playability. Certain notes won't play correctly or even at all because you can't get enough airflow to reach higher notes. After the damage has occurred there are two ways of fixing the issue, soldering a patch over the hole or holes, or replacing the affected part. How can you prevent this from happening? Yearly cleanings. I ask customers to imagine myself as their dentist. Cleaning kits are your instruments "tooth brush" and players need to brush their teeth on a regular basis. Once or twice a year, depending how often you play, you bring the instrument in for its deep cleaning.