system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do people only go bald on their head?

Its not like peoples legs or something go bald only the head.
gpt
Testosterone gets converted by 5-alpha reductase to DHT. DHT causes hair to fall out through its effects on the hair follicle. Because 5-alpha reductase is found in only a few places in the body (scalp for one), DHT is only present there are as well and its effects are localized.