The red or pink part of your lips is called the vermilion, sometimes referred to as the vermilion zone. It’s the soft, colored tissue between the regular skin of your face and the wet mucosa inside your mouth. The vermilion is technically a type of skin, but it differs from the skin on the rest of your body in several important ways that explain why lips look, feel, and behave so differently.
The Four Zones of the Lip
According to the National Institutes of Health, the surface of the lip is made up of four distinct zones: hairy skin, the vermilion border, the vermilion, and the oral mucosa. Each zone has a different structure and function.
The hairy skin is the normal facial skin surrounding your mouth. Moving inward, you hit the vermilion border, a thin rim of paler skin that marks the boundary between your face and the colored part of the lip. On the upper lip, this border curves into the shape known as Cupid’s bow. The vermilion itself is the red part you see when you look at someone’s lips. And behind it, on the inner surface that stays wet inside your mouth, is the oral mucosa.
The transition point between the vermilion border and regular skin is sometimes called the “white skin roll” in surgical and anatomical contexts. The line where the vermilion meets the inner mucosa is called the “red line.” The corners where your upper and lower lips meet are called the oral commissures.
Why Lip Skin Looks and Feels Different
The vermilion is structurally unlike the skin on your cheeks, forehead, or anywhere else on your body. It has no hair follicles, no sweat glands, and no sebaceous (oil) glands. The outer protective layer, called the stratum corneum, is much thinner than on regular skin, and it’s only partially keratinized. Keratin is the tough protein that makes the outer layer of your skin a strong barrier against the environment. With less of it, your lips are more exposed.
The tissue itself is also organized differently. In the vermilion, the tiny finger-like projections that connect the outer skin layer to the tissue underneath (called rete pegs) are narrow, long, and slender. On normal facial skin, those same projections are shorter and blunt. This structural difference affects how the lip surface interacts with the blood supply just beneath it.
Why Lips Are Red
The characteristic color of your lips comes from three factors working together: lower levels of melanin (the pigment that colors and protects skin), thinner surface cells, and a dense network of tiny blood vessels sitting close to the surface. Because the vermilion is so thin and contains less pigment, the red color of blood flowing through those capillaries shows through.
This color naturally changes with age. Research published in the Journal of Cosmetic Dermatology found that both the area and the number of blood vessels in the upper lip vermilion decrease over time. Chronic sun exposure accelerates this process by breaking down the structural tissue around those blood vessels and triggering ongoing inflammation, which leads to the gradual fading of lip color that many people notice as they get older.
Why Lips Dry Out So Easily
Because the vermilion lacks oil glands and sweat glands, your lips have no built-in system for keeping themselves moisturized the way the rest of your skin does. Sebaceous glands on normal skin produce an oily substance that helps lock in moisture. Sweat glands contribute to the thin film that keeps skin hydrated. The vermilion has neither.
On top of that, the thin, incompletely keratinized outer layer means the vermilion has lower water retention capacity and weaker barrier function compared to regular skin. Water evaporates from the surface more readily, which is why your lips are typically the first area to feel dry in cold, windy, or low-humidity conditions. Licking your lips makes this worse: saliva evaporates quickly and strips away what little moisture remains.
Sensitivity and Nerve Density
Your lips are among the most sensitive structures on your body, and the vermilion is packed with specialized sensory receptors. Research in the Annals of Anatomy identified multiple types of touch-sensing structures in the vermilion, including Meissner corpuscles (which detect light touch and texture) and glomerular corpuscles. The density of these receptors is higher in the upper lip than the lower lip, with different types concentrated in different areas: glomerular corpuscles cluster toward the center, while Meissner corpuscles are more common near the corners.
These receptors are equipped with specific ion channels that respond to mechanical pressure, helping you detect fine differences in texture, temperature, and touch. This high sensitivity is why lips play such a central role in eating, speaking, and social communication. Interestingly, no sex-based differences were found in the density or distribution of these sensory structures.
Sun Vulnerability
The same features that make the vermilion unique also make it particularly vulnerable to UV damage. With lower melanin levels, the vermilion has far less natural sun protection than the surrounding facial skin. Melanin acts as a biological sunscreen, absorbing UV radiation before it can damage deeper tissue. The thin outer layer of the vermilion offers little additional shielding.
This is why the lower lip, which tends to receive more direct sun exposure than the upper lip, is a common site for sun-related damage and, in some cases, precancerous changes called actinic cheilitis. Using a lip balm with SPF is one of the simplest ways to protect tissue that has almost no built-in defense against ultraviolet light.