The sudden swelling of the lower eyelid of the patient’s left eye may be related to blepharitis, mosquito bites, eye trauma and other causes. 1. Blepharitis: Blepharitis refers to purulent inflammation of the eyelid glands, and under the stimulation of inflammation, patients may experience redness, swelling, pain and other symptoms. 2. Mosquito bites: If a mosquito bites the lower eyelid of the patient’s left eye, it can cause a localized allergic reaction, and the patient’s lower eyelid can become red, swollen, itchy, painful and other symptoms. 3. Ocular trauma: if the patient’s eyes are bumped, squeezed and other ocular trauma, under mechanical stimulation, the patient’s affected area may appear red, swollen, painful and other symptoms, and subcutaneous bruising and other discomforts may also occur. It is recommended that patients with sudden swelling of the lower eyelid of the left eye accompanied by other discomforts should consult a doctor in time to assess their condition and carry out standardized treatment under the guidance of a doctor.