When a three-year-old baby wakes up in the morning with redness in one eye, it is considered that it may be related to allergy, infection and poor rest. 1. Allergy: mites and cotton wool are easy to cause allergies when babies are sleeping. Allergens entering the eye may induce a localized allergic reaction, leading to eye congestion and redness. 2. Infection: frequent rubbing of the eyes with the baby’s hands during sleep may lead to localized infection by bacteria, viruses and other pathogenic microorganisms. Localized inflammatory stimuli can also lead to eye congestion and redness. 3. poor rest: three-year-old babies sleep poorly at night, excessive fatigue can lead to dilation of blood vessels on the surface of the conjunctiva, which may lead to redness in one eye. There may be other reasons for a three-year-old baby to get up in the morning with one eye red, it is recommended to take the baby to the ophthalmology department of the hospital for consultation.