system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do redheads have a different reaction to anesthesia?
gpt
Scientists are actually a little unsure. But in redheads there is a mutation in the gene that governs the release of melanin  which causes tans and darkens hair. Broken gene means no melanin and you get light skin and red hair.

By sheer evolutionary coincidence this same gene is also reused in pain reception. There's lots of genes that have multiple functions like this.

So basically the pain signals are harder to shut down and pain related nerves are a bit overactive. End result is anasthesia doesn't work as well (by about 20%) and redheads can be more sensitive to pain.