I've seen horrific photos of keycap shine:
https://geekhack.org/index.php?topic=74285.0 and I wonder what could be the cause. Some of them look like they were doused with nail polish. Body oils from the fingers' are often pointed to as the culprit, but is there any scientific basis for this? Could there be a more likely the cause?
From my limited layperson's understanding, there's always small amounts of ketones present in the human blood, but much larger quantities are present when fatty acids in the liver are broken down in a process called ketosis. It often occurs as a result of dieting, exercising, but it can be a side effect of a serious medical illness.
Acetone is the simplest and smallest of ketones and a very aggressive ABS solvent. Could the shine on keycaps be a result of ketones released through the pores of the skin? Furthermore, is it possible your keyboard has a health function the iWatch doesn't have, the ability to warn the user of progressive metabolic acidosis? Just a weird thought.