One-month baby blue under the nose, may be due to physiological or pathological factors, physiological factors such as thin skin; pathological factors such as ischemia and hypoxia, etc., can lead to one-month baby blue under the nose. 1. Physiological factors: the baby’s skin is thin and tender, and the color of the subnasal veins is revealed through the skin, making the skin appear blue. 2. Pathological factors: the baby under the nose skin blue, also need to consider whether there is a lack of blood and oxygen problems, when suffering from congenital heart disease, can lead to the baby’s blood supply and oxygen supply is insufficient, so that the skin blue; in addition, suffering from rhinitis, sinusitis baby, there will also be venous reflux obstacles to the performance of the nose, so that the skin under the nose blue. One-month-old babies blue under the nose, 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.