Swelling and pain in the left eyelid may be caused by trauma, infectious inflammation, contact dermatitis and other reasons. 1. Trauma: It may be due to the left eyelid by the external force of direct blow, collision and other causes of local damage, which can appear left eyelid red, swollen, pain and other symptoms. 2. Infectious inflammation: it may be caused by blepharitis, conjunctivitis, etc. Due to the stimulation of inflammation, symptoms such as redness, swelling, pain and increased secretion may appear. 3. Contact dermatitis: it may be an allergic inflammatory reaction caused by the skin of the patient’s left eye coming into contact with pollen, dust and other allergens. Patients may have erythema, edema, pain and other phenomena. Left eyelid swelling and pain can also be seen in other reasons, it is recommended that patients go to the hospital in a timely manner, clear reasons for treatment as prescribed by the doctor, to avoid delaying the condition.