I had it too, and nothing worked. Then I got a prescription lotion (Lotrimin) and that works. In my case, it's a fungus, and it appears whenever it's warm and moist where my testicles come in contact with another part of me, like my thighs. In boxer briefs, in warm weather, the fungus appears lower down on the thigh where the balls are in contact all day.
The Lotrimin only controls it... my doctor said there is not a cure.
Another doctor, a dermatologist, said the symptoms could be lessened if I didn't wear anything to force my balls against my thighs (say, go about all day just wearing a towel wrapped around your waist with no underwear on). Not very practical outside of India or Scotland (Dhoti / Lungi / Kilt are acceptable wear there more or less), so I deal with it with boxer briefs instead of briefs, shower twice a day, apply warm, dry air from a hair dryer to the area after the shower, apply Lotrimin when it gets red, and apply baby powder every day after every shower.
If I didn't work in an office, while I sat at my computer, I suppose I could wear nothing to press my testicles against my thighs and let them hang loose in the air.
