I noticed this mole on the exterior of my thigh 3 years ago on a trip.It is dime sized and almost circular. It usually is light brown and almost unnoticable but once every 6 months or so it becomes darker (sometimes almost black with purplish contours). It becomes slightly raised and at its worst has a leathery texture. When dark, it is slightly itchy and a bit sore. Then... it gradually decreased in shade and rebecomes light brown for months and is only extremely low itch. I have the impression that it swells up if I touch or scratch it, but I'm not sure. The dark period usually last a week or so and lightens gradually to almost gone. Is this benign?