Dust, Sugar, or Food - the basic mechanical facts and cleanliness of musical instruments.
The mechanics of modern musical instruments is very technical and involves a lot of precision movement of small parts which must operate efficiently and properly for an instrument to play correctly. Airborne elements such as dust, moisture from condensation, plus small particles of food or sugar in saliva are just some of the contributors which cause musical instruments to be unclean and the buildup of these elements will adversely effect the mechanical operation when they collect between the extremely small tolerances between moving parts. Sticking valves, keys and slides are common examples. Beginning band instruments offered by reputable music dealers at school band rental nights will have been cleaned, sterilized and regulated as opposed to instruments from other sources.