A hard knot in the anus may be caused by thrombosed external hemorrhoids, perianal abscess and so on. 1. thrombosed external hemorrhoids: thrombosed external hemorrhoids belong to a kind of hemorrhoids, may be due to fatigue after overeating or bad dietary habits; the patient may appear pain, fever, blood in the stool and other symptoms; can be in the doctor’s guidance of hypertonic saline sitz baths, to a certain extent, can play a role in dehydration, so that hemorrhoidal nuclei gradually atrophy. 2. Perianal abscess: Perianal abscess is caused by acute and chronic suppurative infections of the soft tissues around the anus, which generally cannot be cured. Patients should go to the hospital in time to confirm the diagnosis, timely surgical treatment, so as not to delay the condition caused by anal fistula. It is recommended that patients pay attention to a reasonable diet, maintain a light diet, increase nutrition, drink more water, eat more vegetables and fruits rich in fiber and vitamins; prohibit spicy and stimulating food, prohibit the consumption of alcohol and so on. If you have symptoms of physical discomfort, you should go to the hospital in a timely manner, under the guidance of a professional physician, to identify the causes and give targeted treatment.