Until about 5 years ago my legs were covered with thick dirty-blond hair that was actually hard to see unless I had a tan. Then everyone was like, "Whoa! Where'd all that hair come from?"
Assuming it was thyroid related, I went to see my endo. He ran a full bunch of tests and found what he thought was the culprit: My testosterone wasn't dropping with age. IIRC the number he was concerned with had a ceiling of 1055 for 'normal' and mine was 1047. My response was a half-joking, "You mean I'm losing my body hair because I'm so manly?". He laughed and said, "Basically, yeah. But trust me, you'd rather have your testosterone at the high end of normal than the low."
Although I haven;t researched it, I assume this is why my libido and related equipment seem to be the only part of my body working properly nearly 3 years post heart surgery.