4 months of the baby crying at night, may be due to external conditions are not suitable, rickets, colic and so on. 1. unsuitable external conditions: when the sleeping temperature is too high, it will cause the baby to sweat more; or wear diapers stained with urine and feces, will cause the baby uncomfortable, so that the phenomenon of 4-month-old baby crying at night. 2. Suffer from rickets: mostly due to the lack of vitamin D, rickets will cause the baby’s excitability, the main symptoms are irritability, sleep disturbance, excessive sweating, etc., which will cause the 4-month-old baby crying at night. 3. Appearance of colic: colic is related to acute enteritis, abdominal cold, intestinal necrosis and other factors. Due to intestinal distension or intestinal wall smooth muscle spasm, the baby will have obvious discomfort, which will lead to the 4-month-old baby crying at night. The appearance of 4-month-old baby crying at night, there may be other conditions, you can go to the hospital to improve the relevant examination to clarify the situation and take appropriate measures.