Numbness in the hands when crying is due to the occurrence of hyperventilation syndrome. Patients often have accelerated and deepened breathing when crying, resulting in excessive carbon dioxide excretion from the body, causing a significant decrease in the partial pressure of carbon dioxide in the arterial blood, leading to respiratory alkalosis. The sympathetic nerves become excited and various clinical symptoms appear, among which the representative one is numbness of the limbs, sometimes accompanied by perioral numbness, and in severe cases, the patient may have stiffness of the limbs or even convulsions. Hyperventilation syndrome is mainly a case of hyperventilation exceeding the needs of physiological metabolism, without no obvious organic lesions, and may occur whenever there is hyperventilation. It is more likely to occur when the patient has significant anxiety and psychological discomfort, and is also accompanied by a rapid heartbeat, sweating, palpitations, and a sense of respiratory insensitivity to breathing and accelerated breathing again, leading to more severe symptoms.