I differ a bit on the opinion that Janey on what is required for hair regrowth but honestly I also think that depends on the receptor sensitivity of the person in question and also other hormonal factors.
I'm now a pretty big believer in the fact that other hormones such as IGF-1, insulin, prolactin and DHEA can also make things difficult when it comes to regrowing hair.
I'm already on the recovery after a wave of hair loss but it doesn't seem to be as solid and I get this sort of "sine wave" quality to my hair recovering where it improves a lot and then declines, when I look at pictures from my past, it is very obvious from my face that I had a much higher level of circulating estrogen back in my late 20s when I had my first bad hair fall event.
This thread has reminded me sufficiently that it's not just mitigating the effects of testosterone and specifically DHT, but increasing the hair growth inducing properties of estrogen. Comparing myself now to 10 years ago, my estrogen was a LOT higher, so I fully expect to be able to dose myself topically with enough estrogen to manage a systemic increase and induce hair growth and balance out the deleterious effects of testosterone.
Estrogen will 100% help with dry skin and dry scalp/hair, etc, that's one of estrogen's most potent qualities.
I'm basing the things I say on my own genetic development and physiology, my hair has already made an impressive recovery without a ton of circulating estrogen and with my testosterone being higher than I would like. So I feel like if you're in a similar situation to myself and you know your body has at one point tolerated a decent amount of estrogen systemically, you can return to that state with minimal side effects.
I am going to start low and topically, estrogen as a hormone interacts at the receptor level on the skin, meaning you're getting a very quick and potent response from your skin where you apply it (in this case you want to apply it on your scalp). It also takes time for the estrogen to make its way into the bloodstream which gives your body time to start metabolizing it before it builds up too much.
The less you're bombing your bloodstream and your liver with estrogen it has to process, the more of a preferable balance you'll see when applying it if you wish to avoid side effects. As I've said in the past, I've tried progesterone creams and they did absolutely nothing for me, I've used progesterone capsules as prescribed by a doctor and I got about two weeks into taking them every day before I started feeling the symptoms of gyno.
That to me is indicative of the difference that estrogen will potentially have on your body at the systemic level, only that estrogen will absolutely antagonize the effects of DHT where it is applied to the skin, and it will absolutely induce hair growth and produce vasodilatory effects to aid in it. I can always increase my dose, I'm not in the danger zone where I'm freaking out, I have some leeway, so I'm going to start at a low dose, one that my doctor will find acceptable to try without presuming I'll just immediately get side effects and quit.
That aside, I would have to say that the hormonal approach for hair regrowth is primarily going to be estrogen therapy, along with mitigating any other hormones in excess which might be toxic to that regrowth, that's it basically.