system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is the skin on our lips different from the rest of our skin?
gpt
It’s a mucus membrane! The same type of skin as inside of your mouth, inside the vagina, and under the foreskin, but it’s open to the air so it doesn’t stay wet and feels slightly different. 

The exact reason why our lips are a mucus membrane isn’t entirely agreed upon, but the skin looks different because it’s a different type of skin. It’s almost definitely a sex thing, but whether we have noticeable lips because they’re attractive and have selected for the trait with our sexual preferences, or because they make the mouth a more sensitive erogenous zone and that got our ancestors with noticeable lips more play, isn’t 100% agreed upon.