Unilateral eyelid swelling can be caused by mosquito bites, external injuries and eye inflammation. 1. Mosquito bites: may be due to mosquito bites, caused by eyelid allergic swelling, usually accompanied by itching and tingling and other symptoms. 2. External injuries: acute blunt trauma may have caused the symptoms of bruising and edema of the eyelids. If the swelling is simple, no visual function abnormality, no abnormal rotation of the eyeball, you can use cold water towels for ice, after a period of time will be self healing. 3. Eye inflammation: If it is simple eyelid swelling, it may be related to the inflammatory reaction of neighboring tissues, such as sinusitis, dacryocystitis, etc. may cause unilateral eyelid swelling. If it is also accompanied by symptoms such as congestion, redness and swelling, it may be caused by trachoma, chronic conjunctivitis and so on. To summarize, if patients have the above symptoms, or unilateral eyelid swelling repeatedly, they should go to the hospital in time, to clarify the cause of the disease, and target treatment.