Why is it that my penis feel hotter and more humid than the rest of my body?
Though the scrotum is the primary means of keeping the testicles 1 to 4 degrees cooler than the rest of your body, the penis is on the same basic blood flow pathways. It gets longer when you are hot and shorter when you are cold to vary the amount of heat being released. The veins and arteries in the penis are very close to the surface, allowing good heat transfer.
Just as the radiator in a car seems warmer than the hood of the engine compartment, the same can occur with the penis. In reality, the penis is the same or a few degrees cooler than the inside of your body, but it feels warmer than the rest of your skin because the skin over the rest of your body is thicker and more insulated. The surface of most of your skin feels cool because it is isolated from the warmth inside your body (after all, one of its functions is to keep that warmth inside).
Then, too, the genitals are kept covered. This not only concentrates a bit of the heat, but it also slows down evaporation. The pubic hairs also provide some insulation. Therefore the genitals are generally more moist than the rest of your skin, outside of your armpits which are also covered in hair and contain a large quantity of sweat glands.