system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why is Exfoliating good but scratching is bad?
gpt
Exfoliating is usually subtle, even pressure.  Scratching is usually firm and fairly sharp pressure.

Exfoliating is like using sandpaper and scratching is like using a saw.  In addition, the underside of your fingernails is usually not very clean and is a great place for bacteria to grow.  You're potentially breaking your skin (even if only slightly) and introducing bacteria.  Not ideal.