The outline or the border of human lips called vermillion border is a special feature of human body.
This transition line that appears in our face skin is found only in humans and very few mammals. Reason? No one has answer.
Human lips appear red because of the high concentration of tiny capillaries just below the skin.
The arteries and veins that are connected through series of blood vessels called capillaries.
These blood filled capillaries are very close to the skin surface in lip region and lips appears red.