Suddenly swollen eyelids can be caused by mosquito bites, allergies, granuloma and other reasons. 1. Mosquito bites: If you are bitten by mosquitoes when you are not paying attention in your daily life, your eyelids may be swollen suddenly, accompanied by itching and other symptoms. 2. Allergy: contact with allergens in daily life, such as pollen, skin care products, etc., leading to localized allergic reactions in the eyelids, causing sudden swelling of the eyelids. 3. Emphysema: Emphysema is caused by bacterial infection of the eyelid glands, which may lead to sudden swelling of the eyelid area, and may be accompanied by pain and other uncomfortable symptoms. Patients with serious symptoms of sudden swelling of the eyelids are advised to go to the hospital in a timely manner to clarify the cause of the disease and under the guidance of a professional doctor to carry out targeted treatment.