One of our senior forum members (JustAskin) explained a protocol that Dr. Shippen (apparently) pioneered using scrotal testosterone in order to boost DHT. Before I go on, let me say that this information is for men already on TRT (testosterone replacement therapy). Men using injections can often end up with disproportionately low DHT levels and this technique could be considered to help. (I don’t know of a non-TRT man that has been treated for low DHT with normal testosterone levels.)
The guiding principles behind this protocol is that you use a) a scrotum friendly compounded topical cream – more on that below – and b) do careful monitoring to make sure you don’t go too high with the DHT. Another key point: this is NOT something you do daily. According to this poster, he only had to apply this once every 10-14 days and his DHT levels stayed elevated for that time period which was corroborated by followup labs. Of course, work with your physician on that: I am just reporting one case study. Here is JustAskin’s protocol:
“First I tried every day, my DHT went above 3600!
Then I tried every third day, DHT was about 1800!
Then every sixth day, DHT was 500! I stopped completely for 2 months, DHT went back to 53.
Then I tried E9D and DHT was at 85. I went back to E6D and DHT was at 114.
Libido thru the roof but PSA raised 1/2 point. So after talking with Dr. Shippen, My schedule is now: Testosterone Cyp. .15cc. E3D (except on days I use T. Cream, then I drop injection to .14cc.) HCG .09cc. Daily. Testosterone Cream E9D on day of Injection. With this my hang is much fuller, can have sex when I want, and nuts feel tight, full, and warm.” 
SAFETY: No long term studies have been done. It has been done by a number of men on my and other forums and no bad reports to date. You MUST monitor DHT. If your doctor won’t monitor DHT afterwards, then don’t do this protocol.
TARGET DHT LEVELS: See my page on the subject: Target DHT Levels and Physiological Ranges.
WHY NOT USE BRAND TRANSDERMAL TESTOSTERONE? One question that I get from time to time on the Peak Testosterone Forum is if their Androgel or other topical testosterone gel or cream would not better be applied directly to the scrotum? I guess this might seem logical, since the testes are are supposedly the source of the problem and the gel is the medication. However, the logic here just isn’t right for a few reasons:
1. The testosterone from testosterone gels goes straight into the plasma (blood) and reaches the testes only after being circulated just like any other such medication, i.e. it does not just magically shoot straight into the testes.
2. Exogenous (externally applied) testosterone actually will (partially) shut down the testes of even a hypogonadal man. So it is not “curative” in any sense as far as stimulating or “healing” the testes.
3. Most men have secondary or tertiary hypogonadism which means that their problem is not in the testes but rather the pituitary or hypothalamus.
There is another major problem with applying most of the topicals to the scrotum, according to one of our Peak Testosterone Forum members: topical products often contain alcohol in them, which is simply too harsh and drying for the delicate scrotal skin – ouch! For example, Androgel users are cautioned to ” avoid fire, flames or smoking until the gel has dried since alcohol-based products, including AndroGel 1%, are flammable.”  Yeah, that’s a scary thought, eh?
And, just to summarize, this seems to apply to all the big brand name blockbuster testosterone topicals here in the U.S.:
a) Androgel inactive ingredients: “Carbomer 980, ethanol 67.0%, isopropyl myristate, purified water, and sodium hydroxide.” 
b) Testim inactive ingredients: “Inactive ingredients: purified water, pentadecalactone, carbopol, acrylates, propylene glycol, glycerin, polyethylene glycol, ethanol (74%), and tromethamine.” 
c) Axiron inactive ingredients: “ethanol, isopropyl alcohol, octisalate, and povidone.” (Notice that it has two forms of alcohol that are applied to the skin.
d) Fortesta inactive ingredients: “propylene glycol, purified water, ethanol, 2-propanol, oleic acid, carbomer 1382, triethanolamine and butylated hydroxytoluene”
So before you go running off and rubbing your T on the family jewels as an experiment, keep in mind that you might have to explain to the little woman that your testicular rash isn’t really all that serious. I’ll leave you to decide whether or not she will believe you.
ALLEGED ADVANTAGES: I have not been able to verify this from an authority site, but there are two potential advantages to scrotal application of testosterone:
2. Greater Absorption. Only about 10% of the testosterone in a standard topical is absorbed through the skin. Reportedly, this number is much higher and in the 50-70% range when applied to the scrotum.
POTENTIAL SIDE EFFECTS:
1. High DHT Levels. For reasons unknown, topical testosterone applied to the scrotum will greatly increase DHT levels. DHT (dihydrotestosterone) is the testosterone metabolite largely responsible for acne, BPH (enlarged prostate) and male pattern baldness. Of course, if you are low in DHT, then that may be a different story, but potentially sending DHT levels through the roof is probably not a good idea for most men, since it can have as a side effect accelerated hair loss and enlarged prostate.
2. Non-Physiological Distributions. ZRT Labs published an interesting article where they explained that topical testosterones seem to leave very high levels of testosterone (and estradiol) in the capillaries. They felt that this could potentially be dangerous and should be investigated further. I discuss this in my page on The Potential Risks of Testosterone Therapy if you would like more information.
5) Am J Med, 1987 Sep, 83(3):471-8, “Androgen therapy of hypogonadal men with transscrotal testosterone systems”