The lips (Latin: labia) are soft, mobile, reddish in color, and pliable anatomical structures, encircling the opening of the oral cavity. They are a part of the digestive system located anteriorly in the lower part of the face and head right under the nasal cavity. Together with cheeks, teeth, and gums, they form the oral vestibule, the oral cavity’s anterior part. The lips connect the outer world with the oral cavity and digestive system, and they create the oral fissure or the mouth. It is the very first structure in the digestive canal.

Lip anatomy

Lip anatomy consists of two parts - upper and lower body. The superior lip is the upper vermillion body, and the inferior lip - the lower vermillion body. Both lips are laterally connected in the place called oral or lateral commissures forming the corners of the lips. The upper lip’s superior border goes along the nasal septum base, but lower lips along the mentolabial groove. The lips define the boundary called the vermillion border that separate both lip bodies from the facial skin. The white roll or the lip roll is the top of the upper lip, which borders the skin part of the lip. Near the middle of the upper lip, the border goes up and forms two distinct peaks on both sides, called Glogau-Klein points. The vermillion border dips down in the middle of both summits, creating a double curve called Cupid’s Bow. The depth of the Cupid’s Bow varies. Some lips are uniform in shape. Others have very pronounced depression.

From the Cupid’s Bow vertically to the nose’s alar base goes the philtrum, a concavity without some muscle fibers. It connects the upper lips with the nose. Passing vertically along the lateral sides of the philtrum or from the Glogau-Klein points are the philtral ridges or columns, connecting the nose columella with the upper lip. In the center of the upper lip body is a vermillion fullness - the labial tubercle. The nasolabial crease connects the corner of the lip with the lateral nose margin (called ala of the nose) from both sides. When lips are open, two labial frenula are visible inside. The lip mucous part in the midline from the lips goes to the gums and creates superior and inferior labial frenulum.

Lip golden ratio

The ideal ratio of the vertical height between the upper and lower lip is called the golden ratio. The upper lip against the lower ideally should be 1: 1.6. It can significantly vary in different ethnic groups and even within the same ethnic group. 

Lip movements and muscles

Several muscles control lip movements and the oral fissure. The primary lip muscle is the orbicularis oris muscle. Its marginal part closes the mouth while the labial part pulls the lips forward. Elevators of lips such as the levator labii superioris alaeque nasi and levator labii superioris muscle elevate the upper lip. While depressors (depressor anguli oris and depressor labii inferioris muscles) pull the lip’s angle and lower lip down, they also move the lower lip forward. The zygomaticus major and minor muscles pull the lateral commissures up and laterally. And finally, risorius and buccinator muscles again pull the angle laterally.

Lip microanatomy 

The lip bodies are mostly made of connective tissue and skeletal muscle fibers. There are three zones in the lip surface - the outer surface, vermillion known as the transition zone, and the inner surface

The outer surface is covered by skin, while the inner - by mucosa. The place where both parts connect is called the transition zone. 

The skin part contains sweat and sebaceous glands, hair follicles. It has thin keratinized stratified squamous epithelium.

The transition zone is the modified skin that covers parakeratinized (partially keratinized) stratified squamous epithelium. It does not contain glands or hair follicles, but it contains many sensory nerve endings. Because of the lack of glands, the vermillion part does not have the proper protection, and the lips dry out faster, especially on temperature changes. The vermilion zone is red as it contains many capillaries, and it is highly vascular. It connects the skin and the oral mucosa. The mucosa part is lined by thick stratified squamous non-keratinized epithelium, supported by lamina propria made up of loose connective tissue. 

The submucosa contains irregular dense connective tissue, lymphatic and blood vessels, nerves, fat cells, and labial minor salivary glands.

Lip functions

Lips have several essential functions such as food intake, mastication, erogenous function, and articulation. And they are involved in tactile senses and creating different facial expressions.

As lips have many muscles around them controlling the mouth opening, one of the lip functions is helping get food and drinks in the mouth and closing it airtight after food intake to hold the drinks and food inside the oral cavity. Also, lips help make a narrow funnel that allows babies to breastfeed. This suction motion can be used for adults when drinking through the straw. Lips take part in the mastication process by holding the food between lower and upper teeth during the chewing. Another lip function is to help push the food from the oral vestibule next to the oral cavity proper from where food goes to the following digestive system parts. Lips contain a high number of sensory nerve endings, and they take part in the tactile senses. For example, they are sensitive to temperature changes and touches. Because of many nerve endings, it is an erogenous zone. They have a crucial role in kissing, and they represent sexuality and sensuality. Lips also help in the articulation by creating many different sounds. The lips also help to whistle and take part in playing various musical instruments such as saxophone. And finally, they participate in facial expression making. Lips help to express emotions, for example, when a person is smiling.

 Lip neurovascular supply

The lips are very vascular structures with a substantial vascular network providing the arterial supply, as well as venous and lymphatic drainage. 

They also contain a massive amount of sensory nerve endings. The innervation is provided by the nerves of the autonomic nervous system.


The upper lip is innervated by the superior labial nerve arising from the infraorbital nerve. It is a maxillary nerve branch, but the maxillary nerve is the second division of the trigeminal nerve.

The lower lip receives innervation from the mental nerve that arises from the inferior alveolar nerve, which is a branch of the mandibular nerve - the third division of the trigeminal nerve.

Arterial supply 

The superior and inferior labial arteries from both sides of the upper and lower lips provide the arterial supply of lips. All these arterial vessels arise from the facial artery, which is a branch of the external carotid artery.

Venous drainage

The labial superior and inferior veins provide venous drainage from the lips. Next, the veins go to the facial vein and further flows into the external jugular and brachiocephalic veins.

Lymphatic drainage 

Primary lymphatic drainage from the lateral parts of the upper and lower lip is provided by the submandibular lymph nodes, while the lower lip’s medial segment is drained to the submental lymph nodes.

Lip disorders

Many conditions can affect the visual appearance and functions of the lips, causing it difficult to smile or eat. The most common signs of various disorders affecting the lips are changes in lip color, dryness, sores or ulcers, and spots that vary in colors, also rashes, swelling, bleeding, cracked lips with fissures, and various formations inside the lips.

Lip cyanosis 

Lip cyanosis can present as the sign of many conditions such as heart and vascular system diseases or respiratory system disorders. Lip cyanosis occurs when there is not enough oxygen in the blood system or poor circulation, also in freezing temperatures, and in the case of high levels of abnormal hemoglobin forms in sickle cell anemia. It appears as a bluish discoloration of the lips.


It is a common lip inflammation, presenting as fissures and cracked scaly lips, dryness, irritation, and bleeding. It can appear as an isolated or local disorder or as a sign of systemic conditions. Cheilitis locally can be caused by many infections, for example, HIV. Not only infections cause it, but also regular lip licking and chewing, cold and dry weather. Cheilitis can also be caused by prolonged sun exposure. In this case, it is called actinic cheilitis. It can also appear as an allergic and contact reaction to certain substances or drugs. It can present in nutritional deficiencies such as B12 or iron deficiency. In this case, lip inflammation mainly affects only the corners of the lips, causing angular cheilitis. Some systemic diseases such as lupus and diabetes can present as lip inflammation. Diabetes is one of the causes of lip dryness as high blood sugars can cause dry mouth and lips.

Cold sores

Cold sores caused by the Herpes simplex type 1 virus or orofacial herpes simplex. They are also known as herpes labialis or fever blisters. Cold sores usually appear as a group of fluid-filled blisters outside of the mouth - on the lips’ outer or transition zone. More often, blisters present yellow and become dry and scabbed over time. Later the scabs fall off. Cold sores can also present as only one lesion, although not so often. They are very painful, contagious, and come back periodically. Some of the triggers causing recurrent infections are stress, hormonal changes, traumas, certain diseases. 

Canker sores 

Canker sores, also known as aphthae or aphthous ulcers, are the most common causes for ulcers on lips. They are most commonly small oval or round in shape, painful isolated lesions that appear in the inner part of the mucous of the lips involving soft tissue. They appear with a white center and red border. They are caused by stress, major and minor traumas or injuries, certain food types (for example, acidic fruits and spicy food), certain drugs (anti-inflammatory), and allergies, for instance, to particular substances found within toothpaste. Several conditions can make it worse, such as nutritional deficiencies, immune system suppressions. Usually, sores are self-limiting and resolve in one to two weeks.

Oral candidiasis 

Oral candidiasis, also known as the thrush, is a yeast infection caused by Candida albicans. It presents as white or pale yellow patches of the lips, most commonly on the mucous part. Patches can cause a burning or itching sensation. Some of the risk factors for developing the thrush include diabetes or other endocrine system disorders, antibiotic or drug use, poor nutrition, and immunosuppression (e.g., chemotherapy, HIV infection).

Mucous cysts 

Mucous cysts, also known as oral mucocele, can present as small single fluid-containing bumps or swelling in a person’s lips, most commonly found on the surface of the inferior lip. Usually, they are painless, mobile, smooth, round, soft, and located in the inner lip surface. Fluid-filled cysts develop in minor salivary glands when they become plugged with mucus or in the case of a trauma. Most mucous cysts are self-limiting resolving within few weeks.

Lip cancers 

Lip cancer can involve both lips, but most commonly, it presents on the lower lip. As lips are part of the oral cavity, lip cancers classify as oral cancers, and they are one of the most common oral cancers. Some of the risk factors for lip cancer are excessive tobacco and alcohol consumption, ultraviolet radiation and sun exposure without protective agents, immune-suppressive conditions, and human papillomavirus infection. Squamous cell carcinoma is the most common form of lip cancer.

Summary on lips 

What are the parts of your lips called?

Lips have two main anatomical parts - the upper lip and the lower lip. Both lips have three zones forming the lip surface - the outer surface, the vermillion or transition zone, and the inner surface.

What is lip vermillion?

Lip vermillion is the part people know as lips. It is the body of lips, the red part of it.

What is the area under your nose called? 

The area is called the philtrum.

What is between nose and lips?

This part is called philtrum, a concavity without some muscle fibers. It connects the upper lips with the nose. Along the lateral sides of the philtrum there are vertical philtral ridges or columns, connecting the nose columella with the upper lip.

What is the space between the bottom lip and chin called?

It is called the labiomental groove.

What is the white roll of lips?

The white roll or the lip roll is the top of the upper lip, which borders the skin part of the lip. 

What color are lips naturally?

The color of lips can vary in an individual, but they should have a reddish coloration. It can range from light pink to brownish red color.

Why are lips pink?

The lips are pink or red because they contain many capillaries and are highly vascular.

What color are healthy lips?

Healthy lips should have a reddish color. If they are very dark or very light, it can be a sign of a disease.

Are lips muscles?

Although there are a lot of muscles around them, lips are not muscles.

What is inside a lip?

Lip bodies are made of connective tissue and skeletal muscle fibers that are covered by the epithelium.

What lip shape is most attractive?

There is a golden ratio for lip size. The ideal ratio of the vertical height between the upper and lower lip ideally should be 1: 1.6. Also, significantly expressed Cupid’s Bow is considered attractive.

Why do we have lips?

Lips have several essential functions such as food intake, mastication, erogenous function, articulation. They are involved in the tactile senses and facial expressions.

Do lips grow?

No, they do not grow but become smaller as they age.

What are the little balls in your bottom lip?

Mucous cysts can present as small balls in a person’s lips. Usually, they are painless, moveable, smooth, round, soft, and located in the inner lip surface. The other name for them is the mucocele.

Why do I feel a ball in my lip?

Usually, those balls are mucous cysts, most commonly found in the inferior lip’s inner lip surface. Fluid-filled cysts develop in minor salivary glands when they become plugged with mucus presenting as smooth, round, and soft swellings and balls. Usually, they are painless and moveable. The other name for them is mucocele.

Why are my lips blue?

Blue lips or lip cyanosis can be a sign of many conditions such as heart and vascular system diseases. The symptom occurs when there is not enough oxygen in the blood system, also in freezing temperatures.

How do you know if you have cyanosis?

Cyanosis presents as bluish-colored lips.

How does cheilitis look?

Cheilitis is a lip inflammation, most commonly presenting as fissures and cracked, scaly lips, dryness, irritation, and bleeding.

What are dry lips a sign of?

There are several reasons why a person has dry lips, including the dry and cold weather, an allergic reaction, or an infection.

Are dry lips a sign of diabetes?

Although there are many reasons for dry lips, it may be a sign of diabetes type 1 and 2. High blood sugar can cause a dry mouth and lips.