Sudden swelling under the eyes of patients like mosquito bags, may be caused by eye allergies, eye trauma, insect bite dermatitis, etc. Patients may also be accompanied by eyelid itching, pain and other uncomfortable symptoms. 1. Eye allergy: when allergens stimulate the eye, the patient’s eyes will be localized allergic reaction, resulting in eyelid redness and swelling, the patient should avoid contact with allergens, the use of anti-allergy drugs under the guidance of the doctor for treatment, such as loratadine. 2. Eye trauma: If the patient’s eyes are accidentally injured by the outside world, such as impact, etc., eyelid redness, swelling, pain and other uncomfortable symptoms may occur. 3. Insect bite dermatitis: If the patient is bitten by mosquitoes, and skin allergic reaction occurs after the bite process, eyelid redness and swelling may also occur, accompanied by local tingling, itching and other uncomfortable symptoms. It is recommended that patients with significant eyelid redness and swelling consult a doctor to assess their condition and follow the doctor’s instructions for treatment.