Fishy odor in the anus is considered to be related to fecal residue, perianal abscess, anal fistula, and malignant tumors of the anal canal. 1. Fecal residue: If people do not wipe the perianal area clean after going to the toilet, a small amount of fecal residue in the perianal area, the anus is prone to fishy odor. 2. Perianal abscess: Perianal abscess is mostly caused by the infection of the anal crypt, and the anal crypt is easy to accumulate feces, which is manifested as a fishy odor in the anus. Some of the perianal abscesses are also easily accompanied by persistent pain in the perianal area, fever, loss of appetite, urinary difficulties, acute and severe symptoms. 3. anal fistula: anal canal or rectal abscess, postoperative infection, bad habits can cause anal fistula. The patient can be due to the local secretion of purulent secretion and anal odor, some patients also appear perianal itching, pain and other symptoms. 4. anal canal malignant tumor: disease and genetic factors, local chronic stimulation, etc., can be due to cancer cells invade the local tissue ulceration and the phenomenon of fishy smell in the anus. Some patients are also prone to symptoms such as cauliflower-like lumps, stabbing pain during defecation and unclean feeling during defecation. It is recommended that people with a fishy odor in the anus go to a regular hospital for examination in order to clarify the disease and follow the doctor’s instructions for treatment to avoid delays in the condition. Daily attention to keep perianal clean, try to wear cotton, loose underwear, etc..