Technically it's the ratio of estrogen to testosterone. Everyone has estrogen and testosterone, men andwomen. It's the ratio that determines what happens. Normal male level of estrogen and depleted testosterone will cause gynecomastia just as fast as elevated estrogen and normal testosterone. That's why you see older men show signs. Dropping testosterone levels.
It's all about ratio.
True! There are other factors to consider though.
I've done so much research into hormone therapies for medical reasons over the past couple of years it's not funny.
Castration will rid the male body of over 95% of its testosterone production, but the chance of gynecomastia from surgical castration is less than 30% and from medical castration (LHRH agonists, like Lupron or Zoladex) is actually less than 20%. Only about a quarter of estrogen in men is sourced from synthesization in the testes, but in all cases of castration, the overall T/E ratio is still significantly changed...despite a lesser fall in E compared to T...yet only a minority actually grow breasts. So, simply getting rid of most of your testosterone won't necessarily result in gyne.
The rate of gynecomastia for those on anti-androgens (t-blockers like Casodex or Spironolactone, which allow testosterone to still be produced but not latch to its receptors) is over 80% because the original amount of E is still synthesized 'down there.' The ratio is changed to a greater extent.
Taking Estradiol as a supplement while maintaining testosterone production will obviously change the ratio too, but even so, the chance of gynecomastia is only around 65% if the dose is high enough.
For those who undergo hormone therapy as part of their transition journeys, it is always a combination of either castration or anti-androgen, PLUS estrogen. Despite this, there would probably be millions of disappointed trans women around the world who hardly increased a cup size.
Sorry y'all for hijacking the thread! It's a fascinating subject.