Swelling under the eyes in the morning may be caused by drinking too much water, allergic conjunctivitis, heart failure and other factors. 1. Drinking too much water: the metabolism usually slows down at night, especially after sleep, so if you drink too much water before going to bed, it may not be discharged in time, which may lead to puffiness under the eyes in the morning. 2. Allergic conjunctivitis: patients with allergies may experience allergic reactions when they come into contact with quilts, pillowcases, etc., which may result in itchy eyes, swollen eyes and other uncomfortable symptoms, and the patients may experience swelling of the eyelids and other uncomfortable symptoms when they wake up in the morning. 3. Heart failure: heart failure patients because of impaired circulation, blood reflux obstruction, resulting in fluid retention in the tissues, so that patients can be out of the bags of puffy eyes, especially the lower extremities of the performance of swelling. It is recommended that patients with significant eyelid swelling seek medical attention to evaluate their condition and follow doctor’s instructions for treatment.