The function of all surface tissues on the body, including the lips, is to protect the body from the outside environment. Such protection can only be accomplished if the lips are kept healthy. Healthy, flexible lips help us to smile, whistle, and kiss without discomfort, while protecting us from the harmful effects of the sun and wind.
The Lips’ Surfaces and Layers
The lips have three distinct surfaces. The outside surface of the lip is covered with the same kind of skin as on the face. The part that is commonly referred to as the lip is actually the edge of the lip, also known as the vermillion border, and is more darkly or brightly colored than the facial skin. The inside of the lip is a soft moist surface called the mucous membrane surface. It is made of the same type of tissue that lines the inside of the rest of the mouth.
All three surfaces have their own special functions and characteristics. The mucous membrane surface is constantly lubricated with saliva, allowing it to move easily without being bitten or torn by food. The facial skin and the vermillion border, like all skin are keratinized, meaning the surface cells come from the living cells at the innermost layer of the skin, they die and harden to form a tough protective layer.
This tough, keratin-covered outer surface (referred to as the keratinized layer) protects the delicate underlying growing cells from the harmful effects of the environment, most commonly sun (ultraviolet) exposure, and from dying out. If the keratin layer breaks down and peels, then a person has chapped lips. The “Chaps” are the layers of keratin peeling from the surface of the lip and it should be noted that this protective keratin layer is not perfect. Products such as lip balm are designed to help the skin’s natural keratin protect the lips from dryness and sun damage.
Lip texture can range from smooth to rough. The surface of healthy lips is smoother to the eye and to the touch. If the surface becomes damaged, thick, or dried out, the texture and appearance become rough.
Another aspect of healthy lips is that they are flexible as long as they have enough moisture. This flexibility allows them to stretch and move without cracking.
Lip color varies among people. The color of normal, healthy lips is controlled by several factors, including the amount of natural pigment, the thickness of the overlaying skin, and the color of the underlying blood. On almost everyone, the reason the lips are redder and almost always, darker than the face is because the lip’s surface skin is thinner than the facial skin. Therefore, we can see right through the skin of the lips to the blood in the vessels underneath. The thinner and paler the skin, the redder the lips will appear.
There are other reasons the color of the lips can vary, besides skin thickness. For example, blood is only red if it contains a lot of oxygen; as it loses oxygen to the tissue around it, blood turns blue. Therefore, if a person is cold and the blood is not circulating well through the lips, then the lips can appear blue, because of the color of the underlying blood. Think about the appearance of your lips after leaving a cold swimming pool or playing in the snow! The color of a person’s lips can also be pale if they don’t have enough red blood cells; this is why a person with anemia can have pale or blue lips.
Lips come in many shapes, but in all cases, the upper and lower lips join at the sides to create the corners of the mouth. The center of the upper lip, directly under the nose and bordered by two ridges, is called the philtrum. The philtrum is where the lips joined together during embryonic development.