Simply put, it is caused by bacterial infection and then septicemia. There are three main reasons for perianal infection: 1. Anal gland infection: the anal glands open in the anal sinus at the junction of the anal canal and rectum, the anal sinus is funnel-shaped upward opening, easy to damage injury and bacterial invasion and cause infection. Once the anal sinus is infected, it will cause the anal gland to become infected and purulent, and the inflammation will spread to the perianal space. Because of the poor ability of the perianal space to resist infection, the infection is easy to spread in these spaces. 2.Decreased systemic resistance: such as diabetes, old age and frailty, overexertion and decreased resistance of tuberculosis patients, perianal abscesses are likely to occur. 3.Local anal irritation and injury: such as frequent consumption of irritating foods such as chili peppers and alcohol will lead to local congestion of the anal canal and rectum, and the local resistance will be reduced and susceptible to infection. In addition, dry and hard feces rubbing the mucous membrane of the anal canal skin, dilute feces of diarrhea patients falling in the anal sinus leading to obstruction of the anal gland duct, as well as trauma to the anorectum or stabbing the anorectum by chicken, duck and fish bones swallowed with food can lead to infection around the anorectum and formation of perianal abscess.