It’s primarily friction. Think of it like paint. If nothing touches it, it will last a long time. Including water, cleaners, etc. But, if you take sand paper to it, it won’t last long. If we use the hand sanitizer as an example, it really depends on how long the skin cells last on the hand. They fall off naturally. So, we can safely make claims of up to 4 hours. But, someone swinging a hammer all day may only get a couple hours of protection. On the other hand, surface cleaner on the bottom of a desk may last a long time. But, we can safely make claims of up to 30 days.