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Yes, lips are skin—but a heavily modified, transitional form of it. The lip vermilion (the red part) is only 3–5 cell layers thick versus around 16 layers on the rest of your face. It also has far fewer melanocytes, no hair follicles, and no sebaceous or sweat glands, so the dense network of blood vessels just below shows through as red. The thinness and the high density of nerve endings are also what make lips so sensitive and so prone to chapping.
Lips are one of the most striking facial features that we humans possess. They are also incredibly helpful in our lives. What would we do without them? You stretch them to smile when you want to show your inner glee. You smack them to display your immense satisfaction after a great meal. You pucker them to bring out your petulant side. You bite them to show reluctance. Perhaps most importantly, lips give you the ability to display your affection for anyone and anything!
But why are lips so different from all the other skin areas? Why are they red? Why are they so soft? Why are they so flexible and useful for kissing? Let’s try to briefly answer each of these questions.
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Why Are They Red?
The skin on our lips looks clearly different from the rest of our body. That is because it is much thinner in comparison. Most skin on the body has two main layers—the epidermis on top and the dermis below (a fatty hypodermis sits beneath that). The epidermis itself is built up from several sublayers, and its outermost sheet of dead, flattened cells is called the stratum corneum. The stratum corneum is what we touch when we touch our own skin—it is the body’s barrier against the outside world. The deeper part of the epidermis is busy making new cells, and it is also where the melanocytes live—the cells that make melanin, the pigment that gives skin its colour once it has been exposed to the sun.
The lip vermilion, however, has very few melanocytes (roughly one melanocyte per 10–15 keratinocytes, compared to about one per 4 in regular facial skin), so there is hardly any melanin to mask the red colour of the dense blood vessels that crowd the dermis just underneath. Combined with a stratum corneum that is barely there—only a few cells thick—the result is that the bright colour of blood is directly transposed into the soft pinkish-red colour of your lips.
Why Are They So Soft?
The stratum corneum, by virtue of its protective nature, is harder than the other layers of skin. Lips, however, have a very thin stratum corneum. Therefore, they are obviously softer than the other skin areas.
In addition to this, the skin on your lips doesn’t have hair follicles. Hair follicles cover every external part of your body, excluding the palms of your hands and the soles of your feet. They also play a role in preserving the body’s integrity and add to the skin’s characteristic hardness. That being said, the skin on your lips doesn’t have this luxury, and is invariably softer and more vulnerable.
Another factor that adds to the vulnerability of lips is the lack of sebaceous glands. These are the glands responsible for providing moisture to the skin, but lips are left on their own, with their only source of moisture being saliva. This is why lips are much more likely to be chapped if not moisturized adequately.
Lips (as well as the tips of your fingers) have more nerve endings than any other part of your body. Coupled with the aforementioned thinness of the skin, your lips become extremely useful for kissing!
As you can see, lips have evolved differently for us humans. The thing is, no one really knows why! The outline that divides the reddish-pinkness of the lips from the rest of the skin is called the vermilion border. But why is it found only in humans and not other animals? That is a mystery yet to be solved!
