What causes itching around the anus?

Anal eczema in addition to anal itching symptoms, but also accompanied by skin lesions around the anus like changes; more serious mixed hemorrhoids will anal mouth exudate, irritating anal mouth caused itching; anal fistula repeated pus, concentrated liquid irritating anal skin around, also can cause anal itching; Anal itching caused by gastrointestinal parasites, most of which occur at night before going to bed, itching is more significant; another patient also has this condition anal itching significant, but no significant abnormalities, generally diagnosed as anal itching.