Redness and swelling of the skin on both sides of the anus are mainly caused by perianal eczema, anal fistula and relaxation of the anal sphincter. First, the most common is perianal eczema, which is mainly caused by prolonged dampness around the anus. The most obvious symptoms are redness and papules on the skin around the anus, and significant itching, which may break down and exude tissue fluid when scratched by hand. Secondly, perianal dampness caused by anal fistula is an acute inflammatory lesion of the mucosa of the lower rectum due to bacterial infection, resulting in pus exuding from the anus and creating a damp environment around the anus, leading to itching, redness and swelling of the surrounding skin. A variety of reasons cause the anal sphincter to become relaxed, resulting in incomplete closure, and common sense part of the intestinal fluid stool tissue fluid exudes from the anus, causing dampness, redness and swelling around the anus.