I like your input, thanks for posting. I was actually targeting E2's EC50 value, which has not been determined unambiguously but should be around 0.1nM for both receptors (see
here for study links). Check
this earlier post of mine. Actually, applying around 1ng of E2 on the temples is already sufficient to reach such concentrations (also taking fractional absorption into account). However, I agree that this may be a little short-sighted, because I did not consider the hair follicle as a structure (but just the test-tube estrogen receptors). What concentration would you suggest? 1mcg (on the temples) provides 1000 times the EC50 and should saturate every single receptor available. That is pretty huge, because it would allow us to employ a powerful way to maintain (and a slight possibility for regrowth) hair without the cost of usual sides (20% going systemic - 0.2mcg will not give anyone sides. For full scalp coverage, under 2mcg going systemic should be feasible). To clarify, this does not come even close to oral HRT in terms of effectiveness, but it could allow us to get some of the benefits without any of the side effects.
@JaneyElizabeth. I do not know. I think hairloss in most people is multi-faceted with actually a major inflammatory compound that does not originate from androgens. I would guess that the effectiveness of E2 would depend on the "degree of male pattern baldness" that someone has. For pure male pattern baldness, E2 would of course be a winner since it directly opposes androgens in many ways. Probability for regrowth then depends on factors like scalp calcification and probably age. You cannot really predict the severity of that a priori, but microneedling may help breaking up some fibrosis. Reducing systemic inflammation through dietary adjustments is absolutely underrated in my opinion. While it will not have any effect on male pattern baldness on its own, it should speed up (and increase) the effect of treatments. I would postulate that the lower the systemic inflammation, the higher the chances on regrowth on HRT.
The article on locally varying effects of E2 was in one of my previous posts. Since there is never really absence of androgens
in vivo, I think the results cannot be translated to treatments. The study suggested that in hair follicles on the vertex, E2 was actually catagenic. I do believe, however, that E2 is especially effective in
male frontotemporal follicles, since they lack aromatase compared to
female frontotemporal follicles. In short, I believe that topical E2
definitely adds value to any regimen