Hello - thanks for asking your question.
Without examining the lesion, it would be impossible to say what it is. Possibilities would include dermatitis (inflammation of the skin), a fungal infection, or some kind of genital ulcer (i.e. either herpes or chancroid).
I would be evaluated by your primary care physician or dermatologist. Tests for STDs and possible culture of the lesion should also be considered.
The treatment (either steroid creams for dermatitits or an antifungal cream for a fungal infection) would determine on what is found on examination.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Thanks,
Kevin, M.D.
FYI - I will be away from August 1-9th. I will look forward to answering your questions when I return.