Five-month-old babies with blue lips may be caused by congenital heart disease, malnutrition, albinism, uneven skin color and so on. 1. Congenital heart disease: congenital heart disease can cause cyanosis of the lips in some infants and children, and ischemia around the lips can cause blue lips. 2. Malnutrition: anemia, vitamin deficiency, and micronutrient deficiency caused by malnutrition can also cause pale skin and mucous membranes, which can lead to cyanosis and blueness around the mouth and lips. 3. Uneven skin color: The skin itself is darker or rougher, making the color around the mouth and lips uneven, cyanosis, blue or pale black lips. Baby lips blue, it is recommended to consult a pediatrician in time to clarify the specific causes, if necessary, targeted treatment.