The causes of red, swollen and itchy eyelids are usually due to allergic reactions, mosquito bites and conjunctivitis, etc., which require prompt medical treatment once discovered. 1. If the body is more sensitive after contact with allergens, an allergic reaction may occur, such as in the eyelids after contact with animal hair or pollen, it may cause the skin to appear red, swollen, itchy and other symptoms. 2. Mosquito bites on the eyelids may also cause redness and swelling on the eyelids, and may be accompanied by significant itching. 3. Conjunctivitis may also cause the patient’s eyes to become red, swollen and dry, and the eyelids and surrounding skin may also become red and swollen, accompanied by mild itching or pain. Eyelid redness, swelling and itching may also be caused by other reasons, it is recommended that timely medical examination and treatment to avoid adverse consequences.