In most cases, it is not normal for a three-month-old baby to have his head tilted to the left side for a long time, which may be caused by insufficient neck strength, habitual head tilting, congenital strabismus or strabismus, and so on. However, it is a normal behavior if the baby only deviates a little bit occasionally. 1. Insufficient neck strength: the baby’s neck strength is insufficient to accurately control the movement of the neck, at this time you need to train the baby to raise his head appropriately. 2. Habitual head deviation: babies develop the habit of tilting their heads to one side, which can also lead to head deviation to the left side, and this situation needs to be dealt with by intervention in normal times. 3. Congenital tilt: Congenital tilt is mostly related to intrauterine growth disorders, birth injuries and other factors, three-month-old babies can be corrected through manipulation treatment. If the condition is serious, surgery can be performed at a later date. 4. Strabismus: this is a kind of visual impairment, if not timely adjust the vision, the baby will often tilt the head or neck to one side, if necessary, ophthalmology outpatient clinic, follow the doctor’s instructions for treatment. If the three-month-old baby only occasionally head to the left side, it can be observed and followed up, if the three-month-old baby head to the left side for a long period of time, due to a variety of factors, so it is recommended to seek medical attention to find out the specific causes, so as not to delay the diagnosis and treatment of the disease.