system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Why does the skin on male genitals darken?

I was in the shower this weekend with my son (aged 5) after swimming and he awkwardly asked me why mine is darker (than my skin). I had no answer for him. So can anyone answer this for my son who is actually 5.
gpt
You might want to hold off on the explanation.

Your nipples and penis get darker when you go through puberty. The sex hormones cause a surge in Melanin (which is the pigmentation in your hair and skin).