My Husband Has A Red Patch On His Penis. It's

My husband has a red patch on his penis. It's on the shaft of his penis, right under his head. It'd goes all the way around him. He says it doesn't itch and didn't even know it was there until I saw it. He has been battling a rash that started on his belly that spread around to his back and down to one of his legs. We've been trying to home treat the rash wth 1% hydrocortisone cream and benadryl. We are concerned if this is something serious or home treatable.