A rash on any part of your body should be checked out by a physician. There are a few different possibilities of what this could be, but most likely it is treatable. You should have this treated even if it is not causing you any problems at this time. Choosing to have it treated will help prevent it from spreading, and prevent it from being passed on to someone else.
The first possibility that comes to mind is a skin fungal infection. These infections can be very mild and not cause any itching or pain. They can cause the skin to be discolored (often red). They are usually treated with an anti-fungal cream medication. Another possibility is that your rash is an allergic reaction or a skin condition called atopic dermatitis. This can cause a red rash, but most people report severe itching. There are very few STDs that cause this sort of problem.
I suggest that you schedule an appointment with your primary care physician
. He or she can take a close look at the rash and perhaps determine what it is. If there is any question, your doctor
may take a small scraping of skin cells to examine under a microscope. This way you can be sure to get the right treatment.