I had these exact synptoms after lots of jogging/running without underwear (or with loose boxers) outdoors during the hot, humid summer in Houston TX. It was an irritation rash from chafing (a consequence of excessive friction). It went away on its own in a month or so, after minimizing outdoor running (I stopped jogging for a week, then switched to jogging for a shorter time later at night when the weather was cooler, or at the gym indoors with air conditioning).
Hello,
From your symptoms, it looks like chafing. The other possibility is of lichen planus.
Chafing occurs when the skin becomes irritated by the friction caused by rubbing – either against other skin or against a foreign material. Wash the areas several times with fresh water. Do not use any cosmetic products at the sites. You can apply some calamine lotion at the rash as it will help in soothing the skin.Also wear cotton undergarments.Application of mild corticosteroid cream and oral antiinflammatories like ibuprofen/acetaminophen are also helpful.If the symptoms are severe then it will be best to consult a dermatologist.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.