Four months baby sleep on a head of sweat reasons include: physiological phenomenon, improper clothing, lack of vitamin D and so on. 1. physiological phenomenon: baby metabolism is more vigorous than adults, while the sweat glands are mainly distributed in the head and neck, just fall asleep when the baby’s nervous excitability is higher, the head and neck are easy to have sweating, the general baby asleep after there is no longer obvious sweating, is a normal physiological phenomenon, without special intervention. 2. improper clothing: baby body temperature is higher than adults, if the environment is too hot, too much cover will lead to the baby easy to sweat, parents can touch the baby’s back, if the back is warm, then dressed properly, if the hot flashes of clothing is too thick, need to appropriately reduce the cover. 3. lack of vitamin D: if accompanied by easy to wake up at night, irritable, growth retardation, etc., may be vitamin D or calcium deficiency. Four-month-old baby sleep on a head of sweat, there may be other reasons, it is recommended to go to the hospital in time to improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.