A 4-month-old baby’s sleeplessness may be caused by environmental factors or disorders of the biological clock, or it may be caused by the baby’s indigestion or vitamin D deficiency. 1. Environmental factors: If the baby sleeps in a bad environment, such as strong light or high indoor temperature, it will affect the baby’s sleep, thus making it difficult for the baby to fall asleep. 2. Biological clock disorders: some babies sleep for a long time during the day, which will also affect their night sleep, resulting in less sleep or difficulty in falling asleep at night. 3. Indigestion: the gastrointestinal function of small babies is not yet well developed, if usually feeding improperly, eating too much at a time or eating too much, it is easy to indigestion, resulting in the baby’s body is not comfortable, so sleep will also be affected. 4. Lack of vitamin D: If the baby body lacks vitamin D, it will make the nerve excitability increase, make the sleep is not solid, easy to wake up, may also have excessive sweating and occipital baldness and other symptoms. If a 4-month-old baby does not sleep for a long time, it is recommended to actively go to the regular hospital, by the doctor for scientific treatment, so as not to delay the condition.