Suggest Treatment For Light Patch On The Groin Area

I'm a 41 year old male, 5' 10" and about 130lbs. I run, cycle and am generally quite fit. I do use a sun bed occasionally, which might relate to my problem. A few weeks ago I suddenly developed a small light patch in the groin area. It's about the size of a larger coin, quite round and has a slightly darker ring to the rest of me. The skin itself seems fine, doesn't itch or have any other faults, which is why I've been leaving it really, but it's been a while now and hasn't changed at all, so wondered if I should be doing something about it? Thanks Derek