After defecating, my anus is burning.

This phenomenon may be caused by hemorrhoids, anal fissure, intestinal polyps and other factors. You can use warm water to wash local skin to relieve discomfort. If the pain is more serious, you should seek medical examination; if anal fissure is diagnosed, you can use antibacterial anti-inflammatory and analgesic drugs; usually, you need to strengthen perianal skin care to keep it clean and dry.