About two months ago after a very hot rock concert I got a rash on one side of my groin (nothing on genitals). It is very red, but nothing is raised (i.e. no little pimples or the like) and there is no discharge of anything. It is not itchy, not scaly and is only mildly painful. There are red dots clumped very close together. It has almost completely gone away a few times, but always comes back. Hydrocortisone cream seems to work at time, but it's still not going away. It seems to have spread to the other groin, but only to a small extent. None of the pictures or descriptions I've seen match it. ?????
From the symptoms contact dermatitis, sweat dermatitis, folliculitis, hives and heat rash need to be ruled out. Take some antihistaminic like Benadryl or Claritin and apply some calamine lotion on the rash. Also wear cotton clothes and apply a mild steroid cream if the symptoms are severe. If the symptoms persist then please get it examined from 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.