About six weeks ago I noticed a small red patch on the shaft of my penis just below the head (I'm circumcised). It is painless and has stayed constant in size (not spreading), varying slightly in redness with irritation e.g. bathing and contact. I have no other symptoms.

I have been in a monogamous relationship (really!) for two years, and both my girlfriend and I recently underwent a battery of STD tests, including HIV, Syphilis and a Herpes test (for me, on the spot). Everything came back negative.

It seems to get better if kept dry, but comes back after a shower or long days without exposure to the air (I work in the trades and get sweaty for long hours).

I don't seem to match the symptoms of any STD, or ringworm or other fungal infection. I've tried everything from tinea medication to calamine lotion to no avail and am afraid I may be suffering from some heretofore asymptomatic and rare condition.

Any Thoughts ?