What causes a baby's lips to turn purple?

A baby's lips appearing purple may be caused by various factors. Environmental stimuli such as cold temperatures can lead to peripheral blood vessel constriction, reducing blood flow to the lips and causing them to appear purple. Genetic factors may also result in naturally purplish lips in some babies. Additionally, medical conditions such as congenital heart disease and severe pneumonia can affect heart and lung function, leading to hypoxemia, which in turn causes the baby's lips to turn blue or purple. If a baby's lips remain persistently purple, prompt medical evaluation is recommended.