How can testosterone cause both hair growth and loss, and are there other effects that switch?

Factual Questions
1

How can testosterone (‘T’) cause both hair growth and hair loss? Type “testosterone hair” in Google and the top two suggestions are:
testosterone hair loss
testosterone hair growth
I’ve read some stuff but I still don’t get it. Nothing seems to mention the relationship between the two. T is a hormone that causes body hair growth at puberty; at what point or factors does T invert and do the opposite of what it originally is for?

I’ve had lifetime low T, and when I take T treatments (e.g. by an endocrinologist’s prescription, or on a supplement like creatine which as a side-effect raises T availability), I notice the effects that T is supposed to have. It’s a little bit like I’m going through a form of puberty again because I never fully got the hormones to begin with. Like I think my singing voice is lowering a little bit, and I think I notice a tiny bit more hair growth.

Hair growth/loss in and of itself is a minor issue, but my bigger question is: Are there other T effects that will REVERSE themselves at some point? T affects bone density and muscle mass, THOSE are important. Will T always increase those a man’s whole life, or do those reverse or lessen too??

Thanks for the help as always, guys!

2

It is not really reversal or switch of effects … it is different effects in different locations and at different ages. What happens to pubic hair is not the same as what happens to scalp hair, for example … and both are different than those annoying long ear hairs.

The “how” is because what happens as T (or one of its more potent products, like dihydrotestosterone, DHT) hits receptors and what happens as it hits receptors varies by location and age, and changes in local conversion of T to DHT with age that varies by location.

No idea if there are other changes of the impact of the same level of T that occur with age.