The Anatomy of Healthy Lips

The skin is the largest organ of human body, with a total of about 20 square feet in area. The lips are just a small portion of that total, but like the eyes, the lips have a prominent place in our appearance and predominately factor into our interaction with the world. There are distinct differences in the anatomy and physiology of this region compared to the rest of our body, which affects how we treat and care for the lips.

Anatomy of the Skin

To better understand the differences in physiology and the distinct needs of lip skin, it is good to start with a review of typical skin structure. The three main layers of human skin are the hypodermis, dermis and epidermis. The epidermis is the outermost layer, and the dermis is the middle layer that sits between the epidermis and the hypodermis. The hypodermis helps insulate the body, as this layer is where most of the body’s fat resides. The dermis is packed with collagen and elastin. These are the main structural proteins of the skin, which support its overall structure, providing both strength and flexibility. Sweat glands, oil glands and hair follicles all can be found in the dermis. The epidermis is the thinnest layer of skin and is responsible for many important functions like protection from UV radiation and pathogens, as well as keeping the body hydrated.

The epidermis itself is subdivided into four, sometimes five layers. The main type of cell found in the epidermis is the keratinocyte. These cells divide in the lowest layer called the basal layer, and move up through subsequent layers changing their appearance and composition before being sloughed off. This natural turnover process generally takes about four to six weeks. This constant proliferation of skin cells allows for renewal of damaged cells at the surface. The appearance of an additional layer called the stratum lucidum occurs in areas of thick, calloused skin found on the palms of the hands and the soles of feet.

As keratinocytes make their way up through the epidermis, they undergo several key changes in their transition to corneocytes. Corneocytes are flat, plate-like cells comprised on mostly keratin, a strong structural protein that also makes up our hair and nails. Corneocytes make up the uppermost layers of the epidermis, which is called the stratum corneum. Lipids begin to accumulate in specialized compartments known as lamellar granules as keratinocytes mature. These lipids are eventually dumped into the spaces between cells where they are digested by enzymes to create the mixture of ceramides, cholesterol and fatty acids that make up the surrounding corneocytes. This lipid mixture is uniquely organized to efficiently fill the spaces between cells, providing a strong barrier to water loss.

Related: Top Tips for Perfect Lips

Lip Physiology

The distinct line between the lips and the surrounding skin is known as the vermillion border because of its sometimes pink to reddish hue. Thinner stratum corneum and presence of a transparent protein called eleidin, which is also present in stratum lucidum, allows the red color of hemoglobin in capillaries of the dermis to be visible at the vermillion border in lighter skin tones. The color of the vermillion border can vary from pinkish-red to brown depending on skin color. This line is where we begin to see significant changes from the highly keratinized skin that is adjacent to the lips.

Compared to surrounding skin, the stratum corneum of the lips is much thinner. The outer layer of the lips averages about three-to-five cell layers in thickness, while the stratum corneum of typical skin is on the order of 15-to-20 cells deep. The distinct pattern of furrows in the lips creates an imprint called a lip print that just like fingerprints are unique to each individual. In fact, cheiloscopy, the study of lip prints, can be used for forensic identification.

Ceramides constitute the majority of the skin’s lipid “mortar” matrix and are an important factor in the skin’s water-holding capacity. The total amount of ceramides is lower in lips than other areas of the body. Consequently, transepidermal water loss (TEWL) has been measured to be three times higher on the lip than on the cheek.

The lips do not have hair follicles or sweat glands. Sebaceous glands produce an oily, waxy mixture that helps supplement the skin’s innate barrier properties and they are normally associated with hair follicles. However, sebaceous glands not associated with hair follicles, which are called Fordyce spots, and may be present on the upper lip of some individuals.

The lips also contain fewer of the pigment producing cells called melanocytes, and as a result, have less melanin. Decreased levels of melanin also mean less innate UV protection. UV radiation affects the lower lip to a greater extent because it tends to be more prominent on the face. Accumulated sun damage on the lips accelerates the signs of aging and can result in skin cancer. The best way to prevent sun damage is by avoiding prolonged exposure of the lips and skin, wearing protecting clothing like a broad brimmed hat, and applying a lip balm with an SPF 15 or greater helps avoid further damage.

Caring for the Lips

When caring for the lips, it’s important to keep in mind the unique structure of lip skin and the implications for care and treatment. The lips face constant exposure to the environment and unique structure of the lips leaves them less protected and far more susceptible to injury that many other areas of the body.

Chapped lips can be caused by a variety of factors including exposure to irritants, allergic reaction, frequent sun exposure, dry or cold weather, certain drugs and autoimmune conditions.

In addition to painful sensations, an even application of lipstick or other cosmetics can be difficult when lips are dry, irritated, cracked or peeling. Gentle, physical exfoliation with sugar or other mild scrubs can help remove rough, flaky skin. Removal of this dry skin also helps and reduce the desire to pick or bite at dry, flaky skin, which can cause further damage including tears and bleeding on delicate lip skin.

Properly formulated lip balms can keep lips feel smooth and comfortable and are especially important to use when environmental conditions are dry and cold. Unfortunately, the nature of many long-wearing lip-colors can exacerbate dry conditions on the lip, so their use should be minimized when lips are chapped. Application of thicker balms or a lip mask before bed might be better tolerated than during the day and allow for faster recovery.

Lucious Lips

The anatomy of the lips leaves them more susceptible to dryness and harder to protect from environmental insults. Consistent lip care should be part of an overall skin care routine that aims to protect this delicate area and combat chapping, cracking and dryness.

Kelly A. Dobos is a consultant cosmetic chemist and instructor of a course on color cosmetics at the University of Toledo. Kelly has 20 years of expertise in developing both skin care and color cosmetic formulations working for notable brands like Bonne Bell, Purell, and Jergens. She is part of the American Chemical Society’s expert panel for public relations and serves as a subject matter expert for magazines like Allure and New Beauty.