Sudden crying may be caused by physiological or pathological factors. Physiological factors such as uneasiness and discomfort, and pathological factors such as calcium deficiency and infections can cause sudden crying. 1. Physiological factors: when the child is in an unfamiliar environment, there will be a sense of uneasiness, such as parents did not comfort in time, there may be a sudden cry; similarly, the child feels uncomfortable with the external environment, such as too hot, cold, etc., can also cause the child to suddenly cry; in addition, the child has the emotion, but also in the form of crying to attract the attention of parents. 2. Pathological factors: calcium deficiency in children, there will be an increase in nervous system excitability, resulting in children irritable and sudden crying; infections such as purulent tonsillitis, acute gastroenteritis, etc., can cause the child pharyngolaryngolaryngitis, abdominal pain and other discomfort, resulting in children crying; in addition, children with acute abdominal disease such as intussusception, can lead to severe abdominal pain, so that the child to cry. Children suddenly crying, there may be other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.