Are bones generally harder to corrode than human skin?
Acids and bases are considered corrosive in industrial chemical hygiene. While it is true on a technical level that harder tissue (like bone tissue) will be a bit harder to corrode compared to soft tissue (like skin), a corrosive substance that can cause damage to soft tissue will cause enough damage to harder tissue to be a medical emergency; this is certainly true when you have a highly concentrated substance. If in your world, things that are worn on the person are made from either soft or harder tissue, then the harder tissue would provide slightly better protection. But to be absolutely clear, both types of tissue will be eaten away, it's just a matter of how much.

Metal reactivity with acids and bases is nuanced because it isn't just about hydrogen ion reactivity. The alloy known as hastelloy (trademarked name) and tantalum alloys are metals used in industry for corrosive environments. Silver and gold are resistant to some common acids, but not all (e.g. nitric acid will dissolve silver).