4 months old baby always shaking his head may be frightened, vitamin D deficiency, gastrointestinal discomfort and other reasons. 1. Frightened: if the 4-month-old baby is more sensitive, easy to be frightened, after being frightened will not be able to verbal expression, can appear always shaking his head situation, more also accompanied by crying. 2. Vitamin D deficiency: If the 4-month-old baby always stays at home, no sun exposure, resulting in endogenous vitamin D production is insufficient, which can lead to 4-month-old babies appear always shaking their heads, more often accompanied by irritability, sweating more. 3. gastrointestinal discomfort: if the baby’s abdomen is cold, can lead to gastrointestinal dysfunction, the baby feels abdominal discomfort, may be expressed by shaking his head, accompanied by diarrhea and other symptoms. 4 months old baby always shaking his head, may also be other causes, it is recommended to go to the hospital in time to improve the examination to clarify the cause of the disease, to give targeted treatment or standardized treatment.