 [ Symptoms ] what is this rash on my penis  i developed a red rash on the top and underside of my penis i had unprotected sex with a girl about a week ago and we failed to use enough lubrication my penis was red and sore after i had a small skin colored bump for about a month prior to this that i had my dermatologist treat with cantharidin and the next day i noticed that there was a little more irritation the skin in this area is very dry and i have been diagnosed with seborrehic dermatitis on my face and thighs please help dx [ Disease ] i am very sorry but a diagnosis requires an examination    not something that can be accomplished on webmd answers your description is vague and the possibilities are numerous since the penis is covered by skin and you have a dermatologist seeing this professional would be advisable an accurate diagnosis    not a blind guess    is essential to get a patient specific treatment regime in most cases your treatment will involve a prescription medication again not something that can be provided to you on line