Hello, Bloody diarrhea can be due to different causes like infection, hemorrhoids, anal fissure, lower GI bleeding. Although allergic reaction to contents in the detergent you are using can cause itching although just involvement of anal region only makes it related to some other underlying cause.Although in doubt, I advise stop using the detergent for now. I suggest you visit a gastroenterologist, and get yourself examined. Physical examination is necessary. He might suggest some diagnostic tests for further clarification if needed. Depending on the results he will be able to guide you further with appropriate medical management. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Manisha Auradkar, General & Family Physician