Thrombotic external hemorrhoids are primarily caused by inflammation of the anal veins, or by the rupture and thrombus formation of the anal venous plexus due to excessive straining. The main symptoms are a sudden bluish-purple swelling at the edge of the anus or severe pain. The primary cause is usually due to constipation. Therefore, it's important to maintain smooth bowel movements when eating. Increasing the intake of vegetables and fruits and reducing the consumption of meat, while ensuring regular bowel movements, is most crucial.