The common causes of sudden purple lips in infants include respiratory infections, congenital heart disease, food or drug poisoning and other conditions. 1. Respiratory infections: respiratory infections are aggravated by shortness of breath, hypoxemia, and respiratory failure can lead to purple lips. 2. Congenital heart disease: any child with right-to-left shunt congenital heart disease will have purple lips when pulmonary hypertension occurs. 3. Food and drug poisoning: Eating poisonous mushrooms can lead to sudden purple lips, as can drug allergies or drug poisoning. Infants suddenly purple lips, 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.