Swollen eyes of 3-month-old babies may be caused by trauma, allergy, conjunctivitis and other reasons. 1. Trauma: If 3-month-old baby’s eyes are traumatized, it may lead to the appearance of swollen eyes, which may be accompanied by pain, swelling and other phenomena. 2. Allergy: If the 3-month-old baby comes into contact with allergens, such as pollen, dust, animal hair and so on. Allergic reaction of the eyes caused by allergen irritation, then the eyes may be swollen. 3. Conjunctivitis: Because conjunctivitis itself is an inflammatory disease, it is easy to cause 3-month-old babies to have swollen eyes, and there may be redness of the eyes, abnormal secretions and so on. If the symptoms of swollen eyes are serious and accompanied by red eyes, abnormal discharge and other uncomfortable symptoms, you should promptly go to the regular hospital to identify the cause of the disease, under the guidance of professional doctors targeted treatment.