dear, Rash after sex is highly unlikely as a just sex being a direct cause. Here we do need to rule out the possibility of contraception methods not suiting you, if you are using one. For which, I need to know what method do you practice and does the rash appear immediately after the act, or how long following the sex? there is a high possibility as well for it to be just a seasonal topical skin infection, intros case the rash may be associated with bouts of intense urges to itching. Here in this condition. however it may have no relation with the sex at all. meaning, it s exacerbation or appearance will not be in relation to sexual acts or its timings. treatment: if contraception method is the culprit, then in this case I advice you to change the method. if it s an infection of skin, I advice you a itch guard a topical anti fungal ointment, which will cure it within a week. For a definitive dignosis I need to see the lesion, therefore I suggest you show it to a dermatologist. hope I have satisfied your problem. thank you