Hair loss in a four-month-old baby may be due to physiological hair loss or pathological hair loss due to calcium deficiency. If baby hair loss is less, it may be physiological hair loss, mainly because the hair roots of infants and young children are not yet very firmly fixed within the skin, the child sleeps due to the pressure on the head, sweating, shaking the head and other friction easily lead to the child’s hair loss, this belongs to the normal physiological phenomenon, generally after a few months can be restored. If the baby loses more hair, the hair falls out mainly behind the occipital area, accompanied by easy to wake up at night, easy to cry, easy to startle and other performance, consider the possibility of calcium deficiency caused by rickets, children lack of calcium will be easy to shake their heads when sleeping, will lead to the hair behind the pillow and the pillow friction, resulting in the pillow hair thinning, falling off, forming a typical “pillow Baldness”, is the early manifestation of infant rickets. Therefore, four months baby hair loss, most of them belong to physiological hair loss, generally do not need to worry too much, slowly will return to normal; if the baby hair fall more, there are other manifestations of rickets, it is necessary to be timely supplement vitamin D, more sunshine, appropriate calcium supplement symptomatic treatment.