Sudden swelling of the left eye may be caused by allergy, eye fatigue, granuloma, trauma impact and other reasons. 1. Allergy: patients who are allergic to some pollen, dust, cosmetics, etc. may have swollen eyes, and accompanied by eye itching and other uncomfortable symptoms. 2. Eye fatigue: prolonged sleep deprivation, staying up late or looking at things in low-light places can lead to blood circulation disorders in the eyes, causing eye swelling. 3. Eyelid swelling: When bacterial infection occurs in the eyelid glands, it can cause granuloma, which results in eyelid swelling. 4. Traumatic impact: when the patient’s left eye is impacted by trauma, there will be tissue swelling, local bruising, redness and other symptoms. If your left eye is suddenly swollen and cannot be relieved by rest or is accompanied by other discomforts such as itchy eyes, it is recommended that you consult a doctor for examination to clarify the cause and follow the doctor’s instructions.