I am a 40 year old, caucasion male with pretty fair skin. Within the last 6 to 8 months I have developed a discoloration (darkening) of my skin on my legs right next to my testicals, on both legs, in the same shape as my testicals. I am a very clean person and have used things like lufa sponges, lufa cloths and such to try and scrub the darkened skin off but it seems to be every layer of the skin. Is this caused by sweat from the testicals and is there a way to prevent this? Any helpful comments would be appreciated.