There are two things to remember in caring for wind instruments, especially brass instruments. The first is lubrication – and it will not surprise you that we are saying that! The second thing is equally important – cleaning. You might be surprised at what can build up inside an instrument. Salts and acids from saliva are only the beginning, add to that food and sweet particles and the result is what professional musicians have often called “lungs”.
Over time that bacteria filled lungs or gunk can impair the acoustical performance of an instrument. It can cause the instrument to be “blown out of tune”. An accumulation of gunk occurring at a "node" in the wave of a certain tone, will make it sound sharp. If an accumulation occurs where an "antinode" falls the tone will be flat. Gunk accumulation can also occur in and around valves, and their mechanical action will be impaired or cease if this happens.
There are more serious repercussions too - academic studies have shown the potential for such gunk to cause local infections in the mouth, in the gastrointestinal tract, and in the respiratory tract, with some musicians suffering serious lung problems. The image shows the Streptococcus bacteria - an unwelcome visitor in many wind instruments.
Keeping your instrument clean will not only help avoid that, it will also be healthier to play, and it will give it a longer playing life and help to maintain its value. It will also look better and perform better.