system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do blisters form? And what is the purpose of the liquid inside of the blister?
gpt
If you were 5, I'd explain: "Blisters are nature's band aid."  They form to protect the underlying layers of skin from an irritant.  The reason people will tell you to never pop a blister is because the fluid within it is sterile.  Not only that, but our outer layer of skin is our "first line of defense" against pathogens. When you pop the blister, you break that line of defense and release the protective sterile fluid - leaving the underlying layers susceptible to infection.