Hi, An itchy rash there can be an allergic reaction to something(like a lubricant used for the first time, a skin infection or infestation). This is unlikely related to semen. If your partner also had similar itchy rash there before, this can even be scabies, which spread easily with skin to skin contact. For symptomatic relief, you can take levocetirizine 5mg tab at night for 5 days, along with calamine lotion application to soothe the area. If not getting down by 2-3 days, kindly get it examined with your doctor to find out and treat the exact cause. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Muhammed Aslam T. K., Pediatrician