Lip Anatomy: A Complete Guide to Structure and Function
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
The lips (labia oris) are two folds of tissue around the mouth that are essential for speech, eating, and facial expression. They have specialized parts, including the vermilion and the inner mucosa, and are moved by the orbicularis oris muscles. The vermilion has no sweat or oil glands, so regular care and sun protection help keep lips healthy [1].
Quick Answer: What is lip anatomy?
Lip anatomy describes the upper and lower lips, the folds of tissue around the mouth, including the surrounding skin, the reddish vermilion and the inner mucosa. The orbicularis oris muscles move the lips, and lips help with speaking, eating and sealing the mouth. Because the vermilion has no sweat or oil glands, lips are prone to chapping and sun damage. [1]
What the research says
Chronic sun damage of the lip can progress to cancer, which is why lip protection matters. A systematic review of observational studies screened 1,126 articles and found only one that measured malignant transformation of actinic cheilitis; in that study the rate of progression to squamous cell carcinoma was 3.07%. The authors call for more studies and point to higher-risk groups, including people with heavy UV exposure, older males, fair-skinned people, and smokers (Dancyger et al., J Investig Clin Dent, 2018 [2]).
Actinic cheilitis can be treated, and laser had the best results among non-surgical options. A systematic review of 49 papers (789 patients, 843 treated areas) found a complete clinical response in 76.5% of patients and clinical recurrence in 10.2%; laser therapy gave complete response in 244 of 260 patients (93.8%), partial surgery in 14 of 14, and photodynamic therapy in 68.9% with 12.6% recurrence. The studies were heterogeneous and larger studies are needed (Lai et al., J Am Acad Dermatol, 2020 [3]).
What are the essential functions of your lips?
Your lips are specialized structures that work automatically and consciously throughout the day [1]:
Appearance: lips are a key part of how your face looks, which can affect how confident you feel.
Eating and drinking: they take part in eating and drinking, often so automatically that you do not notice.
Communication: they are extremely important for speech and also for wordless cues such as expressions and gestures.
Social interaction: for example, displays of affection such as kissing.
Keeping things out: closed lips form an airtight and watertight seal for the mouth.
What are the structural components of the lips?
The upper lip starts at the bottom edge of where the nose extends from the face, and the lower lip ends where the chin begins to extend forward. Lips have several distinct parts [1]:
Part | Description |
|---|---|
Skin | The skin between the mouth and nose and between the mouth and chin; it has sweat and oil glands and hair follicles. |
Vermilion | The reddish-orange part most people mean by "lips"; color varies with skin color. It has no sweat or oil glands and gets moisture from sources like saliva. |
Philtrum | The small dimple between the upper lip and nose. Its lower curved edge, where the vermilion begins, is called Cupid's bow. |
Mucosa | The part of the lip inside the mouth, lining the inner walls that rest against the teeth and gums. |
Labial commissures | The creases at the corners of the mouth, where the upper and lower lips meet. |
Labiomental groove | The small groove or crease between the lower lip and the chin. |
The main parts of the lips: vermilion, philtrum, Cupid's bow, labial commissures, and labiomental groove.
Muscles and Nerves
The main muscles that control the lips are the orbicularis oris muscles, which form an oval under the skin around the mouth. They do not attach directly to the skull; instead they attach to other facial muscles, especially those around the cheekbones and chin. The facial nerve carries signals that move the lips, while the trigeminal nerve carries touch sensation from the lips to the brain [1].
The orbicularis oris muscle surrounds the mouth and supports speech, eating, and sensation.
What are common lip conditions and their warning signs?
Lips are prone to many conditions, from lip-specific problems to those that affect skin in general [1]:
Injuries: bruising, swelling, or splitting.
Chapping and cracking.
Infections: cold sores (fever blisters) from herpes simplex virus, infected pimples, infected hair follicles, and canker sores on the inner lip.
Skin conditions: eczema and actinic cheilitis (sun damage).
Structural and serious conditions: cleft lip and lip cancer.
Lip conditions often cause changes you can see or feel, such as color changes, pain, itching, swelling or growths, changes in firmness or texture, and cracking or peeling. Persistent growths or sores that do not heal should be checked, because they can be a sign of lip cancer [1][2].
How are lip conditions diagnosed and treated?
Your dentist is often the main person to help manage lip health and usually examines your lips during routine visits. A primary care provider can also help, especially with conditions of the lip skin, and may use swab cultures or a tissue biopsy when needed. Treatments depend on the problem and can include stitches for some injuries, creams or ointments for infection or irritation, and reconstructive surgery for larger injuries or congenital conditions such as cleft lip [1].
How should you care for your lips?
Caring for your lips means protecting them from the sun, staying hydrated, avoiding irritants such as licking or picking, and treating chapping early.
Protect from the sun: use lip balms that contain sunscreen, since sun damage can lead to actinic cheilitis [1][2].
Stay hydrated: drink enough water [1].
Avoid irritants: do not lick, bite, rub, or pick at your lips, and be selective about what you put on them [1].
Treat early: avoid chapping or treat it quickly to prevent deeper cracking [1].
Common lip conditions and everyday care tips.
What is the bottom line on lip anatomy?
Your lips combine muscles, nerves, and specialized tissues that make speaking, eating, and expression possible. Knowing their structure and the signs of common problems helps you protect them and get care sooner. Regular care and routine checkups with your dentist or primary care provider are the best way to keep your lips healthy.
Your next step: if you notice persistent dryness, a sore that will not heal, or unusual changes in color, swelling, or texture, see your dentist or primary care provider for an evaluation [1].
Frequently Asked Questions
What is the medical term for lips?
The medical term is "labia oris" or simply "labia." The upper lip is the labium superior and the lower lip is the labium inferior.
What is the vermilion?
The vermilion is the reddish-orange part of the lip that most people think of as the lip itself. It has no sweat or oil glands, so it gets its moisture from sources like saliva.
What does the philtrum do?
The philtrum is the small dimple between your nose and upper lip. It is part of the facial structure and its lower curved edge forms Cupid's bow.
Which muscle controls the lips?
The orbicularis oris muscles, which form an oval around the mouth, are the main muscles that control the lips.
Why do lips get chapped so easily?
Because the vermilion has no oil or sweat glands, it cannot stay moist on its own and is easily dried out by the environment.
What is Cupid's bow?
Cupid's bow is the curved lower edge of the philtrum, where the vermilion of the upper lip begins.
Can lips get sunburned?
Yes. Sun damage to the lips can cause a condition called actinic cheilitis, and lip balms that contain sunscreen help protect them.
What are labial commissures?
Labial commissures are the creases at the corners of your mouth, where the upper and lower lips meet.
How do lips help with speech?
Lips are extremely important for speaking. They help make sounds and form words by changing shape and position.
When should I see a doctor for a lip sore?
See a dentist or healthcare provider if a sore is persistent, changes color, swells, grows, or does not heal.
Related Reading
What Are Chapped Lips? Dry, Cracked Lips Explained explains why lips get dry and cracked and how to heal them.
Cold Sore: Stages, Causes, Triggers, and the Treatments That Shorten an Outbreak covers the virus behind cold sores and how outbreaks are treated.
What Is Cleft Lip and Cleft Palate? Symptoms, Causes, Diagnosis and Treatment explains this common birth difference of the lip and its repair.
Lip Cancer: Symptoms, Causes, Risk Factors, and Treatment Options Explained describes warning signs of lip cancer and how it is treated.
References
Cleveland Clinic. Lip Anatomy. Cleveland Clinic. February 27, 2026. https://my.clevelandclinic.org/health/body/lip-anatomy
Dancyger A, Heard V, Huang B, et al. Malignant transformation of actinic cheilitis: a systematic review of observational studies. J Investig Clin Dent. 2018;9(4):e12343. PMID 29863311. https://doi.org/10.1111/jicd.12343
Lai M, Pampena R, Cornacchia L, et al. Treatments of actinic cheilitis: a systematic review of the literature. J Am Acad Dermatol. 2020;83(3):876-887. PMID 31400450. https://doi.org/10.1016/j.jaad.2019.07.106
Medical disclaimer
This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. The clinical information in this guide reflects source material last reviewed in February 2026.
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