Puffy lower eyelids in babies may be caused by physiologic factors such as excessive water intake, change in body position, or pathologic factors such as conjunctivitis, allergies, and kidney disease. 1. Physiological factors (1) Drinking too much water: the eyelid area has loose tissue, when the body has water and sodium retention, excess water tends to enter the tissue space in the eyelid area, which is manifested as puffiness in the eyelid area. If the baby drink too much water and milk at night, coupled with the baby’s own kidneys on the body’s water regulation ability is weak, easy to appear puffy. (2) position change: if the baby keeps the head low sleep position at night, due to the effect of gravity, the body’s water will also enter the loose eyelid tissue, can also appear eyelid swelling. 2. Pathological factors (1) Conjunctivitis, allergy: conjunctivitis and local allergic reaction will make the patient’s local capillary expansion, congestion, tissue fluid leakage into the loose tissue of the eyelid interstitial space, manifested as eyelid edema. (2) Kidney disease: Kidney is an important organ for water and salt regulation in the body. In renal diseases such as nephritis and nephrotic syndrome, the kidney’s ability to regulate water and salt is weakened, which leads to sodium retention in the whole body, manifesting as generalized edema in addition to eyelid edema. It is recommended that children with significant eyelid swelling should seek prompt medical attention to assess their condition and follow medical advice. If your baby has lower eyelid swelling that does not resolve over a long period of time, you should seek medical attention to identify the cause of the swelling and follow the doctor’s instructions for targeted treatment.