Most men know that DHT (dihydrotestosterone) is largely responsible for male pattern baldness and, all too often, that's about all they know. This can lead to tragic consequences as we will show below, because it is just assumed that only testosterone is the "Male Sex Hormone".
However, nothing could be further from the truth. Below we are going to show you some of the huge benefits of DHT, many of which will be very reminiscent of our old friend testosterone:
1. Orgasm Frequency. One study examined a variety of sex hormones in male military personnel (the estrogens and testosterones). The researchers found this surprising fact: the only one that was related to orgasm frequency was DHT. In fact, the authors stated that "an increase in concentration of 1.36 nmol/l (about 2 SD) corresponded to an average increase of one orgasm a week." Nice, eh?
2. Sexual Function and Morning Erections. Yet another study found that giving topical DHT to senior men with low or lowish testosterone levels lead to dramatic improvements in sexual function.  For example, both morning erections and the ability to maintain an erection were improved by the supplemental DHT. Again, limiting DHT does not sound like such a good idea.
3. Regular Erections. Again, an animals study showed that both testosterone and DHT were effective at restoring regular erections in castrated animals. 
4. Libido. One interesting animal study showed that castrated animals given DHT (and a metabolite of estrogen) had indistinguisable sexual behavoirs from castrated animals given testosterone. In other words, the down stream metabolites, or byproducts of testosterone (which includes DHT) can be as powerful as testosterone itself. 
This list could go on as DHT is involved in penile neuronal activity as well: it play a very key role in the development of both penis and prostate for example. So you get the idea: this is not a good hormone to mess with and DHT is definitely a "Sex Hormone" as well.
NOTE: You may also be interested in my link on How to Increase DHT (Naturally and Otherwise) for some additional information. For example, there are a few supplements and dietary means to raise DHT more naturally.
Unfortunately, this is a lesson we all had to learn the hard way. Two drugs came out to treat BPH (enlarged prostate) and hair loss. The thinking at the time was that DHT was responsible for both and so finasteride (Propecia) and dutasteride (Avodart) for BPH and hairloss (off label in the case of dutasteride) were created as 5-alpha reductase inhibitor. As many of you probably know, 5-alpha reductase is the enzyme that converts testostosterone into DHT and so someone got the bright idea that reducing DHT would be a miraculous cure for men everywhere.
Did you know you can inexpensively do your own testing for most hormones? The industry leader is Discounted Labs..
Instead, we have found these medications to a disaster and many men have what is termed Post-Finasteride Syndrome, which is permanent or near permanent loss of testosterone with related symptoms including nipple soreness, mood disorders, gynocomastia, etc. Some of the men that have shown up on The Peak Testosterone Forum have complained of this syndrome and attribute their hypogonadism to prior Propeica use. For example, look at the comments of this poster:
"I just recently encountered your article regarding Post-Finasteride-Syndrome, and I could share some advice from my own experience and recovery processes. I started taking the drug, in the Proscar form, about a year ago when I was 18. My doctor prescribed it to me, and unfortunately, neglected to warn me of the potential consequences. Of course, just two weeks in, I began to experience the described sexual side effects including numbness, shrinkage, testicular pain, dysfunction, etc. I stopped taking the drug immediately, but things only seemed to get worse. After a month off, my system "crashed", causing severe androgen deficiency and I was experiencing the full myriad of sexual and mental side effects, so add depression, fatigue, anxiety, insomnia, lack of motivation to the list of symptoms." 
This poster was able to partially recover his testosterone, but many men have not been so lucky and seem to suffer permanent damage. This issue I have actually covered in some detail in a link called The Risks of Propecia Use. The point, though, is that DHT is intimately tied to your libido and sexual function and this is something that doctors do not adequately explain to their male patients. Often by the time they give you the medication, it is too late.
Let's move, though, to another issue that concerns many men going on HRT (Hormone Replacement Therapy or testosterone therapy): hair loss. The reasoning behind the concern goes like this: some testosterone is converted into DHT via 5-alpha reductase and thus, if you increase testosterone levels through testosterone therapy, you will increase DHT as well. This, it turns out, is true. For example, one study of men on pellets, standard injections and testosterone undecanoate noted that "5Î±-dihydrotestosterone (DHT) levels appeared to parallel those of T on the three forms of therapy."  In other words, as testosterone went up, so did DHT.
However, it is a huge stretch to say that simply because DHT increases that one's hair will fall out. In fact, here are a few facts to consider:
1. Steroid users, who push their testosterone levels artificially high, do not report acclerated male pattern baldness.
2. None of the HRT users on The Peak Testosterone Forum have complained of hair loss.
3. I know of no study that forewarns men on testosterone therapy to be concerned about greater risk for hair loss on HRT.
Does this mean that HRT never causes hair loss? No, it very likely does in some sensitive inidividuals and it is an occasionally reported side effect. So, if you're really worried about your hair, talk to your physician first and get his or her insights. I do know that if the side effect occurs to you, the stats don't matter. In addition, you may want to check out these links on Hair Loss Factors and Hair Loss and Male Pattern Baldness.
1) Testosterone Undecanoate (Nebido). In the above study, testosterone undecanoate did lead to the highest levels of DHT. 
2) Scrotal Patches. And in the U.S., Testoderm has a scrotal testosterone patch that may lead to elevated DHT with respect to other forms of testosterone therapy. One small study examiningg scrotal testosterone patches concluded "that transdermal [scrotal] testosterone therapy is an effective long term treatment for hypogonadism in men. It is, however, associated with high serum DHT levels, whose potential long term effects on the prostate and other tissues need to be investigated."  This is also verified by a study where topical testosterone rubbed on the scrotum led to greatly increased DHT levels. See my page on Testosterone Therapy and the Scrotum for more details.
1) BMJ, 1995, 310:1289, "Contribution of dihydrotestosterone to male sexual behaviour"
2) The Journal of Clinical Endocrinology & Metabolism, Apr 1 2002, 87(4):1467-1472, "The Effects of Transdermal Dihydrotestosterone in the Aging Male: A Prospective, Randomized, Double Blind Study"
4) Clinical Endocrinology, Aug1984, 21(2):97-107, "WHICH TESTOSTERONE REPLACEMENT THERAPY?"
5) Science, 19 Octr 1973, 182:283-285, "Copulation in Castrated Male Rats following Combined Treatment with Estradiol and Dihydrotestosterone"
6) Physiology & Behavior, Mar 1980, 24(3):463â€“468, "Hormonal regulation of penile erection in castrated male rats"
7) The Journal of Clinical Endocrinology & Metabolism, March 1 1988, 66(3):546-551, "Transdermal Testosterone Therapy in the Treatment of Male Hypogonadism*"