Why would any of us guys want to boost our DHT? After all, DHT (dihydrotestosterone) in us males is created from testosterone via the 5-alpha reductase enzyme and, therefore, most men with decent testosterone also have decent DHT levels. Furthermore, if you ask almost all physicians (that even care) how to boost your DHT, they will tell you that you should do it via HRT, which will raise both testosterone and DHT simultaneously. In spite of these points, I have seen on The Peak Testosterone Forum some legitimate reasons for wanting to raise HRT. Quite often men that are interested have the following situation:
--Average or midrange testosterone levels
--Below range or near below range DHT levels
The reason that these men are so concerned is because DHT plays a major role in libido, something I discuss in my link on Testosterone and DHT. So it is reasonable to assume that below average DHT could be playing a role. And DHT can also serve to limit estradiol, so some men are concerned that low DHT could lead estradiol-related symptoms. For example, there is some evidence that low DHT can lead to certain kinds of gynocomastia. In addition, some men also simply do not like the idea of standard HRT for a variety of reasons and feel that DHT is a safer and less instrusive way to go
CAUTION: In my opinion, you only want to consider DHT under a doctor's supervision and with adequate monitoring. And the primary reason is that too much DHT could lead to accelerated hair loss. What if Mother Nature already gave you a buzz cut? Well, too much DHT could also lead to acne and hair growth. Some say that it could enlarge the prostate as well. This is questionable, though, because DHT actually blocks estradiol and it is the latter that is most associated with prostate enlargement according to many experts.
Here are some Ways to Increase DHT Naturally:
1. Scrotal Testosterone. Okay, I said I would avoid HRT in this discussion. However, scrotal testosterone is a bit different. Basically, there is a (admittedly small) study out there that shows that rubbing testosterone on the scrotum leads to a higher conversion rate to DHT than normal.  The authors noted that applying testosterone to the scrotum lead to
"The serum testosterone and estradiol levels did not rise above the normal adult male range at any time during therapy. However, elevated serum dihydrotestosterone (DHT) concentrations occurred during treatment; the pretreatment DHT concentration was 95 +/- 3 ng/dL (3.3 +/- 0.1 nmol/L), and it increased to 228 +/- 40 ng/dL (7.8 +/- 1.4 nmol/L) after 4 weeks of treatment and remained elevated thereafter."
This is a large boost in DHT and, therefore, great care should be taken for reasons mentioned above. (Of course, talk to your physician first.)
NOTE: There are also oral DHT's out there. For example, Winstrol, stanololzol, Proviron and other medications are oral, synthetic DHT's. You can also buy DHT in gels - Andractim for example - but this is only available in certain countries.
2. Topical Testosterone. Dr. Crisler has stated several times that he prefers topical or transdermal testosterone preparations, because they boost DHT a little more proportionately. So, if you're a man on standard testosterone therapy (TRT or HRT), then this might be another route to go. You do have to be very careful around women and children if you use this option.
3. Creatine. One study shows creatine to be a solid DHT booster. Furthermore, this was shown to be true on young, male rugby players who should have beefy DHT levels to start with. The study showed that DHT levels increased to 56% above their starting point and settled in at 40% above baseline at the two week point.  How creatine does this is not known, but it is apparently NOT by increasing testosterone. This same study showed no significant increase in testosterone but found that the T-to-DHT ratio increased by 22% after two weeks. If you are wondering about dosage, the study gave these young men the standard "gym dosage" of 5 grams daily.
Creatine has many other benefits including increasing workout output and satellite cells (for muscle building). Be careful if you have any existing kidney disease and be sure to consume some extra water throughout the day.
CAUTION: 21 grams daily of creatine led to huge (450%) increases in urinary formaldehyde.  Normal daily dosages are 5 grams but even modest increses in formaldehyde are potentially dangerous, because formaldehyde is a likely carcinogen. 
4. Protein/Carb Ratio. There is also a study out there that shows that you can alter the conversion of testosterone to DHT with just diet alone. Here are the macronutrient levels in this particular study:
"The volunteers were fed a high protein diet for 2 weeks and then a high carbohydrate diet for a second 2-week period; there was an interval of 3 weeks between the study periods during which they consumed their usual home diets. The high protein diet consisted of 44% of calories as protein, 35% as carbohydrate and 21% as fat; the high carbohydrate diet consisted of 10% of total calories as protein, 70% as carbohydrate, and 20% as fat." 
So notice that both of the diets had, at least for the typical American, fairly low levels of fat and essentially the researchers were playing with the protein/carb ratio. So diet #1 was with a protein-to-carbohydrate ratio of about 1.25 and diet #2 had a protein-to-carb ratio of 0.14. Of course, as a guy who lifts weights and eats a lot of protein, I would like to believe that the higher protein diet was superior. However, that was not the case and, in fact, the higher protein diet actually lowered DHT and it did so by lowering the activity of the 5-alpha reductase enzyme that converts testosterone to DHT. The authors noted that "the isocaloric substitution of protein for carbohydrate in the diet decreased the delta4-5alpha-reduction of testosterone while concurrently increasing the oxidative metabolism of estradiol and also of antipyrine in man."
Again, I consume a lot of protein, but I do this with "eyes wide open." I discuss some of the potential issues in my page on Dangers of Protein for those interested.
5. Zinc. If you are zinc deficient, the evidence shows that it can be a root cause for low DHT. Furthermore, if this is your underlying issue, you can significantly raise your DHT just by taking this inexpensive supplement. Try to avoid the zinc oxide form, since it is so poorly absorbed. For some of the studies, see my link on Zinc and DHT. (A zinc deficiency can also lead to very low testosterone levels as well.) I do have some cautions though about taking too much zinc and I urge anyone taking supplemental zinc to scan through this page: The Potential Dangers of Zinc.
5. Oral DHEA. There is For details on this study, see my link on What Hormones Does DHEA Change Anyway? page.
6. Exercise. If you are fairly inactive, exercising my increase your DHT significantly. One study followed a 100 sedentary men after putting them on a one hour per day (6 days per week) exercise program. Their DHT increased from their baseline by 14.3% at the 3 months point and 8.6% at 12 months.  Not bad for something that will boost you nitric oxide and help you lose weight, eh?
7. MEN ON TRT: Once a Week Transdermal. Some men on testosterone cypionate (or enanthate) injections may have DHT levels a little too low and their libido may not be where it should be. On this page I discuss a clever solutions that one of our senior posters mentioned that Dr. Shippen is using: Low DHT While on Testosterone Injections.
NOTE: If your doctor does not do enough monitoring due to insurance and cost considerations, see my page on Inexpensive Testosterone Labs. I have no affiliation with any of these, so, of course, do your own due diligence.
1) Clin J Sport Med. 2009 Sep;19(5):399-404, "Three weeks of creatine monohydrate supplementation affects dihydrotestosterone to testosterone ratio in college-aged rugby players"
2) PNAS, Dec 1983; 80(24):7646 7649, "Nutrition-endocrine interactions: induction of reciprocal changes in the delta 4-5 alpha-reduction of testosterone and the cytochrome P-450-dependent oxidation of estradiol by dietary macronutrients in man"
3) J Clin Endocrinol Metab, 1988 Mar, 66(3):546-51, "Transdermal Testosterone Therapy in the Treatment of Male Hypogonadism"
4) Med Sci Sports Exerc, 2008 Feb; 40(2): 223 233, "Effect of Exercise on Serum Sex Hormones in Men: A 12-Month Randomized Clinical Trial"
5) Med Sci Sports Exerc, 2005 Oct, 37(10):1717-20, "Effect of oral creatine supplementation on urinary methylamine, formaldehyde, and formate"