Swelling under the left eye may be related to physiological factors, or it may be caused by trauma to the left eye, allergy to the left eye, or blepharitis of the left eye. 1. Physiological factors: If the patient’s left eye is bitten by mosquitoes, the toxins secreted by mosquitoes are retained in the local skin, which may cause the patient’s left eye to be swollen, and the eyelid itching and other discomfort. 2. Trauma to the left eye: If the patient’s left eye is accidentally traumatized in life or work, it may cause swelling under the left eye, which may be accompanied by symptoms such as inability to open the eye, pain and other discomforts. 3. Left eye allergy: If the patient’s left eye comes into contact with allergens such as pollen, cosmetics, dust mites, etc., it may cause an allergic reaction in the left eye, which may lead to swelling under the left eye, and may be accompanied by itching, congestion and other uncomfortable symptoms. 4. Left eyelid blepharitis: If blepharitis occurs in the left eye, under the stimulation of inflammation, the patient’s eyelids may appear red and swollen, and the patient may also be accompanied by tearing, foreign body sensation and other discomforts. It is recommended that patients with significant eye swelling consult a doctor to evaluate their condition and follow the doctor’s instructions for treatment.