Why are our lips so red, so sensitive and dry so quickly? For which evolution awarded us with these features?
The lips contain about 1 million nerve endings, so they are so affected by touch, as well as changes in temperature and humidity level. The skin of the lips outlines the boundary between the skin of the face and the mucous membrane of the inside. The mucous membrane is represented by a large area in the sensory cortex of the brain and therefore very sensitive. Because of this, lips are capable of subtle and accurate muscle movements.
This ability to subtle and accurate movement, provided by five muscles for lifting the lips (upward movement) and four for lip depression (downward movement), allows people to communicate and pronounce the entire set of vowels and consonants that are in our languages.
Why are the lips red
The skin of the lips with three to five cell layers is very thin compared to typical skin of the face, which has up to 16 layers. In the light color of the skin, the lips contain less melanocytes (cells that produce melanin pigment, which gives the skin its color). Accordingly, nothing interferes with blood vessels flowing close to the surface of the skin of the lips, give them a bright red color.
With darker skin color, this effect is less noticeable, because in this case the skin of the lips contains more melanin and, therefore, visually darker.
The lips, like the soles of the legs and palms of the hands, do not have hair follicles, so the hair cannot grow there. This is because these parts of the body are more effective without hair – it would be much more difficult to grab objects if our palms were hairy, while our lips with hair would be less effective in pronouncing words.