@Caillou
No one should be taking any 5a-reductase inhibitor for hair loss without understanding what causes hair loss (and then they shouldn't take it anyway because it will be counterproductive in the end). I'll tell you exactly why this happened.
Hair loss is not androgen mediated. Testosterone does not cause hair loss. DHT does not cause hair loss. If you think about it, it doesn't even make logical sense. What happens as we age? We produce less steroids and our expression of steroid metabolizing enzymes is reduced or defiled in some way. Younger people are more potent and more virile... their rate of steroid synthesis is higher and their steroid receptor sensitivity is higher than those who are older and if androgens were the cause of hair loss, then most teenagers should have severe hair loss and we don't see that.
In reality, what's happening is that you're losing expression of 5AR and aromatase enzymes in the skin and hair follicles due to the presence of (likely) estrogens where they don't belong (in circulation). You want estrogens and other specialized steroids in the tissues they belong and not in circulation. If their concentration in circulation is too high, the estrogen receptors (or androgen or progesterone, etc.) in hypothalamus are over-activated and the hypothalamus cuts off steroid synthesis and aromatase expression by down-regulation of gonadotropin releasing hormone (GnRH), lowering pituitary luteinizing hormone (LH) and follicle stimulating hormone (FSH) (lowered FSH contributing to lowered aromatase expression).
Low intrafollicular synthesis of estrogens causes hair loss in
both men and women. It's the same root cause for both, but manifests differently in men compared to women. There are two reasons for this:
1. Men generally (but not always) have a higher expression of 5AR in the skin and hair follicles. 5AR and aromatase are both competing to metabolize substrate (e.g. testosterone, androstenedione). If 5AR expression dominates aromatase expression in the hair follicles, guess what you end up with a deficiency in? Estrogens. It's not DHT causing the issue, it's poor enzymatic expression... 5AR is dominating aromatase expression and the binding affinity between androgens and 5AR is much higher than between androgens and aromatase. So, in men hair loss can be much more severe because they can have two things working against them: high 5AR expression drawing away androgens and leaving too few behind for sufficient aromatization, and low aromatase expression. Occasionally, you'll see men that have more of a female pattern loss and it's because they have the underlying low intrafollicular aromatase expression, but normal 5AR expression.
2. Hair loss manifests differently in women because they generally don't have high expression of 5AR in the skin or hair follicles. So, their problem strictly resides in their inability to produce sufficient intrafollicular estrogens caused strictly by poor aromatase expression. This is why their loss will manifest in a global diffuse pattern. Their entire scalp is deficient in aromatase expression so a global thinning occurs. 5AR expression in men causes an additional problem which results in more rapid loss of hair on the areas of the scalp that are more prone to insufficient blood supply.
Men have the added problem of 5AR in conjunction with (likely) low aromatase expression. As the condition progresses, tissue fibrosis worsens and blood flow further suffers, causing an even greater deficiency in intrafollicular estrogens, nutrition, and clearance of spent steroids. It seems to me that estrogens have a protective effect in the skin, either by protection against inflammation, increase in elasticity of skin, or both.
So, back to 5a-reductase inhibitors and why they won't work. When you cut off an entire metabolic pathway like 5AR, you're going to get a very sharp increase in concentration of upstream hormones like testosterone, androstenedione, progesterone, deoxycorticosterone, aldosterone... any steroid that takes that pathway is going to pool... it's going to become stagnant because there's no flow. There are many ways in which this is incredibly unhealthy, but let's just focus on what happens when testosterone and androstenedione are cut off from the 5AR pathway. Testosterone, for example, will pool. It will sharply increase in concentration and, because of this, you will experience a temporary sharp increase in estrogens. This is just reaction kinetics... probability... there's more testosterone and now that 5AR is not a viable pathway, the only player in the game is aromatase. So, this is actually the reason why finasteride or dutasteride have ANY positive effect on hair loss. They will cause a temporary increase in estrogen synthesis via metabolism of those pooled androgens. The problem is that while this is happening, it's also happening in the hypothalamus and it's job is to do whatever it takes to get your blood concentration of estrogens down to the safest level it's capable of. So, it down-regulates its secretion of GnRH and causes lower overall steroid synthesis (making you steroid deficient, not just androgen deficient) as well as reduced aromatase expression.
So, by taking dutasteride, you actually worsened your problem by lowering your body's ability to produce steroids and also lowering it's expression of aromatase. Both of these thing reduce estrogenic activity in the follicles... reduced aromatase is obvious, and reduced steroid synthesis just limits the substrate available that can be aromatized.
The best thing anyone can do for both their hair and their health is to get your body to produce naturally higher levels of steroids and naturally higher levels of steroid metabolizing enzymes like aromatase (and even 5AR). If your body is synthesizing steroids at a higher rate and expressing higher levels of aromatase, it's because you have a better metabolic throughput. In other words, your body makes steroids, those steroid are transported to the cells of specialized tissues, those steroids are used, and then they're metabolized further and eliminated or reused appropriately. When they're not metabolized and dealt with properly in the tissues they're made in, then they end up in circulation and cause hypothalamic down-regulation. Aside from being healthier and getting your body to produce higher levels of steroids, scalp massaging, needling, and anything that can reverse tissue fibrosis and promote elasticity and blood flow will help.
For those that experience hair loss, I believe it's possible to reverse it and have a full head of hair, but it's not ever going to be easy. You have one or multiple genetic shortcomings that make having hair a full time effort, while others can eat trash and have awful habits and have a thick head of hair all the way until the day they die.