Upper Facial Muscle Balance: Frontalis & Brow Depressors
[Asymmetry Series: Part 2A]

By Jude Harford

BNurs (Hons), PgDip (Adv Practice), NMIP

Nurse Practitioner, skinByJude

Jude is a prescribing aesthetics nurse practitioner with a strong interest in menopausal skin health and regenerative treatments. Her focus is on achieving natural results through evidence-based practice using the highest quality product

• Website: https://skinbyjude.co.uk/
• Instagram: https://www.instagram.com/skin_by_jude/

This article continues our multi-part clinical guide on upper facial dynamics. If you missed the foundation, review Part 1: Treating Facial Muscle Asymmetry with Botulinum Toxin.

Introduction

Assessment of the upper face extends far beyond identifying the muscle responsible for an individual wrinkle. Every movement of the brow, forehead and periocular region represents the combined action of multiple muscles working in harmony. Dynamic asymmetry therefore rarely arises from dysfunction of a single muscle in isolation. Instead, it reflects an imbalance between muscles with opposing or complementary actions, often influenced by compensatory movement patterns, structural anatomy and the ageing process.

For the aesthetic practitioner, this distinction is fundamental. It is tempting to focus attention on the eyebrow that sits higher, the eyelid that appears more hooded, or the forehead that wrinkles more deeply. However, these visible findings are often the consequence of altered muscle balance elsewhere. Successful treatment therefore begins not by identifying where the asymmetry is seen, but by understanding why it has developed.

This principle becomes increasingly important as practitioners move beyond standard aesthetic treatments and begin managing facial asymmetry. Unlike routine treatment of forehead or glabellar lines, asymmetry requires a detailed understanding of functional anatomy, careful observation of dynamic movement and an appreciation of the compensatory mechanisms that develop throughout life. Small differences in muscle activity may have a disproportionate effect on brow position, eyelid appearance and facial expression, meaning that conservative, well-reasoned treatment is generally preferable to aggressive correction.

It is also important to recognise that not all asymmetry is muscular in origin. Apparent differences in brow height or eyelid position may reflect underlying skeletal asymmetry, dermatochalasis, variations in skin elasticity, previous surgery, facial nerve dysfunction or age-related changes in soft tissue support. The role of botulinum toxin is therefore confined to correcting dynamic muscular imbalance; it cannot correct structural asymmetry and should never be expected to do so.

Throughout this section, the emphasis will be on developing a logical approach to assessment. Rather than considering each muscle independently, practitioners are encouraged to assess the upper face as a coordinated functional unit, recognising the interaction between brow elevators, brow depressors and periocular muscles before deciding whether treatment is appropriate.

Functional Anatomy of the Upper Face

The upper face is often described anatomically as a collection of individual muscles, yet clinically it behaves as an integrated biomechanical system. Brow position, forehead movement and eyelid appearance are determined by the balance of forces generated by several muscles acting simultaneously. Understanding these relationships is considerably more valuable in clinical practice than simply memorising the origin, insertion and action of each individual muscle.

At rest, the position of each eyebrow represents an equilibrium between muscles that elevate the brow and those that depress it. During facial expression, this equilibrium changes continuously as different muscle groups contract with varying degrees of intensity. Even subtle alterations in one component of this system may influence the appearance of the entire upper face.

Unlike many skeletal muscles, the muscles of facial expression insert directly into the dermis rather than into bone. Their primary role is therefore not movement of joints, but movement of the overlying skin to produce facial expression. Because these muscles interdigitate extensively and frequently overlap, weakening one muscle inevitably alters the forces generated by neighbouring muscles. This explains why treatment of one anatomical region may produce visible changes elsewhere, sometimes beneficially and sometimes unintentionally.

The Brow Elevator

The frontalis is the only true elevator of the eyebrows. Originating from the galea aponeurotica and inserting into the dermis of the forehead and eyebrows, it raises the brows, creates horizontal forehead rhytides and contributes significantly to facial expressions of surprise, attentiveness and curiosity.

The frontalis demonstrates considerable anatomical variation between individuals. The two halves are often asymmetrical in both muscle bulk and recruitment, and in some patients the muscle fibres are separated centrally by a broad aponeurotic interval. Differences in muscle strength are therefore common and should not automatically be regarded as pathological.

Importantly, frontalis activity frequently reflects compensation rather than primary overactivity. Patients with heavy brows, dermatochalasis or mild eyelid ptosis often subconsciously recruit the frontalis to elevate the eyebrows and improve their superior visual field. This compensatory contraction may occur unilaterally if one eyelid is more hooded than the other, resulting in apparent frontalis asymmetry. Failure to recognise this adaptation may lead to treatment that reduces an important functional mechanism, leaving the patient with heavier brows or increased eyelid hooding.

The Brow Depressor Complex

Opposing the frontalis is a group of muscles collectively referred to as the brow depressor complex. This consists principally of the corrugator supercilii, procerus, the orbital portion of the orbicularis oculi, and, where present, the depressor supercilii.

Rather than acting independently, these muscles function together to lower the eyebrows, draw them medially and contribute to expressions of concentration, anger or concern.

The corrugator supercilii pulls the medial brow inferomedially, producing the characteristic vertical glabellar rhytides. The procerus contributes primarily to inferior displacement of the medial brow while creating horizontal lines across the bridge of the nose. The orbital fibres of the orbicularis oculi assist in brow depression, particularly laterally, and play an important role in forceful eyelid closure.

In many patients, asymmetry of the brow is more accurately explained by unequal activity within this depressor complex than by differences in frontalis function. A relatively stronger corrugator or orbicularis oculi on one side may hold that brow in a lower position despite symmetrical activity of the frontalis. Appreciating this relationship is essential when assessing brow height and planning treatment.

The Periocular Muscles

The orbicularis oculi deserves particular consideration because of its multiple functional roles. Encircling the palpebral fissure, it contributes to blinking, forceful eyelid closure, lacrimal pump function and lateral brow depression. Age-related changes, habitual facial expression and previous neuromodulator treatment may all influence its resting tone and recruitment.

Asymmetry of orbicularis oculi activity may manifest as unequal crow’s feet, differences in eyelid closure, narrowing of one palpebral fissure during smiling, or asymmetrical brow position. However, practitioners should be cautious not to attribute every apparent difference in eye size to orbicularis activity alone. Variation in globe position, eyelid anatomy, dermatochalasis and true ptosis must also be considered.

Muscles Rarely Work Alone

One of the most important concepts in upper facial assessment is that no muscle should be considered in isolation. Facial expression results from coordinated activation of multiple agonists, antagonists and synergists. Weakening one component inevitably alters the mechanical balance throughout the region.

For example, a patient presenting with one elevated eyebrow may appear to have unilateral frontalis overactivity. Closer assessment may instead reveal relatively stronger brow depressors on the contralateral side, compensatory frontalis recruitment due to ipsilateral dermatochalasis, or long-standing skeletal asymmetry. Although the visible finding is identical, the underlying mechanism—and therefore the most appropriate treatment strategy—is entirely different.

Similarly, a patient complaining of unilateral eyelid hooding may demonstrate increased frontalis recruitment on that side in an attempt to elevate the brow and improve the visual field. In this situation, reducing frontalis activity without addressing the underlying cause may worsen the patient’s symptoms despite technically accurate treatment.

The role of the practitioner is therefore not simply to identify which muscle contracts most strongly, but to understand how the entire upper facial musculature interacts to produce the patient’s appearance. This functional approach forms the basis of safe, predictable and natural-looking treatment and should underpin every assessment of upper facial asymmetry.