system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If skin doesn't pass the scratch test with steel, how come steel still wears down after a lot of contact with skin (e.g. A door handle)
gpt
Can’t scratch is not the same as can’t damage.

Every time your skin contacts a piece of steel, it’s leaving behind oils and moisture.

The oils and moisture can chemically corrode the steel surface ever so slightly, forming iron oxide.

While iron oxide is still harder than your skin, it’s also weak, porous, and brittle. The next touch or cleaning can wear it off, exposing clean steel that can be corroded and eroded again.

It might only be a few molecular layers at a time but over hundreds of thousands of uses the wear adds up to a noticeable amount.