 [ 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 ] psoriasis is a chronic skin problem that causes skin cells to grow too quickly resulting in thick white silvery or red patches of skin this commonly affects skin of the scalp and over the knees and elbows but can occur anywhere on the body about 10 to 30 of people with psoriasis develop psoriatic arthritis psoriatic arthritis may develop at any age but usually affects people between the ages of 30 and 50 while the cause is not known genetic factors along with the immune system likely play a role in determining who will develop the disorder