Im not sure we know for sure, but I think under certain circumstances both could play a role. I think though largely its DHT that is the main player but again its your hair sensitivity to androgens that is the problem even if you have little DHT it could be enough. I for instance have very little body hair, but when I was in early college I had zero facial hair and body hair. Over years as I got more thicker facial hair my head hair also very slowly miniaturize over time. I think hair is very sensitive to small amounts of androgens maybe even T in some cases.