The lips are divided into several distinct anatomical zones, each with unique function and characteristics.
The Vermilion
The vermilion is the visible pink-red area of the lips. Unlike typical skin, it:
• contains very little melanin
• has a thin keratin layer
• contains a dense network of capillaries close to the surface
This lack of pigment and thin skin allows underlying blood vessels to show through, creating the characteristic lip colour.
The vermilion border forms the sharp outline between the lip and surrounding facial skin. In aesthetic treatments, this border is important for defining shape, symmetry, and contour.
The Philtrum and Cupid’s Bow
The philtrum is the vertical groove extending from the upper lip to the base of the nose, bordered by two philtral ridges.
The Cupid’s bow is the curved central contour of the upper lip.
Together, they contribute to:
• lip shape
• facial youthfulness
• aesthetic harmony
With age, these features may flatten due to volume loss and reduced dermal elasticity.
The Oral Commissures
The oral commissures are the corners of the mouth.
They are clinically important because they are:
• prone to drooping with ageing
• associated with marionette lines
• areas where saliva pooling can occur
Downturned commissures can create a “sad” or tired facial expression even at rest.
Lip movement and expression are controlled by a complex group of facial muscles, most of which insert into the orbicularis oris.
Orbicularis Oris — The Primary Lip Muscle
The orbicularis oris is a circular sphincter-type muscle surrounding the mouth.
Functions include:
• closing the lips
• pursing and puckering
• speech articulation
• kissing and expression movements
It consists of superficial and deep fibres that interlace with other facial muscles. Over-activity or tension in this muscle may influence perioral lines.
Supporting Expression Muscles
Several muscles contribute to lip elevation and smiling:
• Levator labii superioris — lifts the upper lip
• Zygomaticus major and minor — raise the corners of the mouth (smiling)
• Risorius — retracts the corners of the mouth
• Levator anguli oris — elevates the mouth corners
Muscles responsible for lowering the lips include:
• Depressor anguli oris — pulls the corner of the mouth downward
• Depressor labii inferioris — lowers the bottom lip
• Mentalis — elevates and wrinkles the chin, everting the lower lip
These muscular interactions explain why emotional states are so easily expressed through subtle lip movements.
The lips are highly vascular structures.
They are primarily supplied by:
• the superior labial artery (upper lip)
• the inferior labial artery (lower lip)
Both branch from the facial artery.
High vascularity:
• contributes to lip warmth and colour
• enables rapid healing
• increases bruising risk in injectable treatments
Vessel depth varies by region, making anatomical awareness essential in clinical contexts.
The lips are rich in sensory nerve endings, allowing high tactile sensitivity.
Innervation includes:
• Infraorbital nerve — supplies the upper lip
• Mental nerve — supplies the lower lip
• Branches of the facial nerve — control expression muscles
This explains why the lips are highly responsive to touch, temperature and pressure — and why discomfort may be more noticeable during procedures.
While the face has typical epidermal layers, the vermilion border is unique.
The lip surface contains:
• thin epidermis
• minimal sebaceous glands
• no sweat glands
This contributes to:
• increased dryness
• susceptibility to cracking
• sensitivity to environmental exposure
Hydration and barrier protection are therefore clinically relevant in skincare practice.
Ageing produces visible and structural changes in the lips, including:
• thinning of the vermilion
• flattening of the Cupid’s bow
• reduced definition of the vermilion border
• volume loss due to fat and collagen reduction
• lengthening of the upper lip
• development of fine perioral lines (“barcode lines”)
• downward turning of oral commissures
These changes alter both function and aesthetic appearance, influencing treatment planning in cosmetic settings.
A detailed understanding of lip anatomy supports:
• safe treatment planning
• realistic client expectations
• natural aesthetic outcomes
• ethical and evidence-informed decision-making
It is especially important in contexts such as:
• lip treatments and rejuvenation procedures
• advanced skincare assessment
• ageing and facial anatomy education
• professional beauty practice
Knowledge of anatomy underpins clinical reasoning and ethical treatment selection, rather than focusing on cosmetic enhancement alone.
The lips are complex, functional, expressive and clinically significant anatomical structures. From speech and eating to expression and aesthetics, they play a central role in communication, identity and facial harmony. For practitioners working in beauty, aesthetics or skin science, developing a strong understanding of lip anatomy supports safer practice, improved assessment skills, and more informed professional decision-making.
Learn more about Lip Anatomy in the Advanced Learning Academys on line Lip Anatomy course. Click
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