Hi Dear, Understanding your concern. As per your query you have symptoms of red mark, tender and sore inside butt crack which are due to allergic reaction or body s response to external stimuli which can be a allergen. There are number of factors that can cause this like milk, eggs, peanuts, medicines, insect bites and stings. Need not to worry. I would suggest you to try to figure out what exactly causing red blotches in your case , give cold compresses to affected area to get rid of itching. Avoid itching and pricking rashes and apply betnovate cream on them. You should take benadryl and consult dermatologist for proper diagnosis doctor will take history and prescribe steroid medicines . Hope your concern has been resolved. Best Wishes, Dr. Harry Maheshwari