I found out some interesting facts while studying our lips:
- They are covered in glabrous skin, while most of the skin surface is hairy;
- The outermost layer (stratum corneum) of the skin is far thinner than on any other part of our body;
- They lack pigmentation (melanin);
- Their pink colour is due to underlying capillaries.
- Their only source of moisture is our saliva. They lack sebaceous gland;
What is the reason behind this specialization of our lips?
Why is it not covered with the thicker skin type found elsewhere on the body? The lips are not more sensitive than the fingertips for example (see figures below), i.e., the pressure thresholds are similar (upper graph) and the two-point discrimination thresholds as well (lower graph).
Source: Institute Balseiro