system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does your lip differ from your face or your skin, and why?
gpt
They still have all the layers of skin, but the outermost layer is thinner. Lips also have no sebaceous glands, so saliva is the only natural way to moisten lips. And lastly, lips have no melanin, so the color you see is from blood vessels.