Cold exposure can increase testosterone levels, potentially by increasing blood flow to the testes during rewarming.

“sounds pretty crazy, but believe it or not, that and things like ice baths and cold showers can have positive effects on the sex steroid hormones, both testosterone, mainly in males, and estrogen, mainly in females”

“the most plausible explanation for why cold exposure, either through 1 to 10-minute ice bath or cold shower or the ice underpants thing, would increase testosterone or increase estrogen is that you're cooling the neurons that control vasoconstriction and vasodilation and shutting down the entry of blood, or at least reducing it, and hormones into the gonad, and then when the gonad and the surrounding area heats up again, you're getting a rebound hyper-vasodilation that delivers excessive levels of, not excessive, but increased levels of GnRH and other hormones and carriers and so forth that would then stimulate the gonad to release more testosterone or would stimulate the gonad to release more estrogen, that's the most plausible explanation I can come up with”

“The other probably more likely mechanism relates to the dopamine increases caused by cold exposure that we talked about earlier. Again, anytime you have a somewhat stressful stimulus, but in particular with cold exposure, it seems that the catecholamines, norepinephrine, epinephrine and dopamine all increase and dopamine is known to be in the pathway that can stimulate testosterone. And so while there isn't a direct relationship between dopamine stimulating testosterone, there is an interesting pathway way whereby dopamine increases can trigger increases in things like luteinizing hormone, which can trigger increases in testosterone as well as estrogen for that matter.”

“The first is somewhat direct, which is that anytime you cool a body surface, that if it's cold enough, you're going to get vasoconstriction. And then subsequently you're going to get a rebound increase in vasodilation, meaning you're going to constrict the blood vessels in that area. And then after the cold is removed, there's going to be more blood flow to that area.”

“I think it's very likely to increases a number of different hormones.”

“You know that there are products on the internet, and there are actually a few decent manuscripts looking at how cold exposure can increase testosterone levels, but it doesn't happen by the cold directly. Good scientists, as the authors of those papers, were and are, realized that it's the vasoconstriction and then the vasodilation. As people warm up again there's increased blood flow to the testicles, and in women it seems there's probably increased blood flow to the reproductive organs as well after people warm back up. So that seems to cause some sort of hyper nourishment of the various cells, the Sertoli and Leydig cells of the testes that lead to increased output of testosterone and in women testosterone as well.”

“cooling the testicles leads to increases in testosterone which is on the face of It kind of um counterintuitive because turns out that it's about the Vaso constriction causing the subsequent increase in blood flow increased Vaso dilation”

“what happens is there's a rebound in vasod dilation after cooling so cooling causes Vaso constriction and then after the cooling there's a rebound vasod dilation and there's more infusion of blood into the gonads”