Simply put, it is caused by bacterial infection and pus. There are three main causes of perianal infection: (1) anal gland infection: the anal gland opens in the anal sinus at the junction of the anal canal and rectum, and the anal sinus is funnel-shaped and opens upwards, making it easy for damage and bacterial invasion to cause infection. Once the anal sinus is infected, it will cause the anal gland to become infected and septic, and the inflammation will spread to the perianal space. Because of the poor ability of the perianal interstitium to resist infection, infection can easily spread in these interstitium. (2) Decreased systemic resistance: such as diabetes, old age and weakness, overexertion and decreased resistance in patients with tuberculosis, which are prone to perianal abscess. (3) Local anal irritation and injury: such as frequent consumption of irritating foods such as chili peppers and alcohol can lead to local congestion in the rectum of the anal canal, and local resistance is reduced and susceptible to infection. In addition, dry and hard feces abrading 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.