What could cause purple swollen lips?

Many causes. Purple lips, also known as cyanosis in medical terminology, is caused by the discoloration of the skin and membranes. The area that is affected by cyanosis appears to be bluish in color. Though purple lips can be caused due to cold weather, it can also be a cause for concern, as it may be a symptom of underlying diseases related to the heart and respiratory system.
Cyanosis. Purple lips also known medically as cyanosis. It can be cause by extreme cold. More serious condition that cause this can be related to the heart and respiratory system.