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The science of nerve and muscle signalling

How relaxer treatments work.

Understand the connection between nerves, muscles and expression lines, and how botulinum toxin temporarily changes that signal.

Explore the mechanism ↓

Movement first. A personal plan.

A small junction with an important role.

A facial expression begins with a nerve signal. At the point where a motor nerve meets a muscle, a chemical messenger called acetylcholine passes that signal on. Relaxer medicines reduce its release from selected nerve endings, so the treated muscle contracts less strongly.

How do nerve signals and muscle relaxers work? →

Nerve → chemical messenger → muscle

How the mechanism works.

Nerve endingMuscle
Before treatment
Acetylcholine is released from the nerve ending and reaches receptors on the muscle, helping trigger contraction.
Nerve endingMuscle
After the medicine takes effect
Less acetylcholine is released at affected nerve endings, reducing activation of the selected muscle.

Simplified educational diagrams created for this guide. They are not injection maps and do not show dose, placement or a predicted result.

1. Binding and entry

Botulinum toxin type A binds to particular structures on the nerve ending and is taken into it. The action occurs on the nerve side of the nerve, muscle junction.

2. Changing messenger release

Inside the nerve ending, its active component cleaves SNAP-25, a protein involved in the machinery that releases acetylcholine. Fewer messenger-containing vesicles can release their contents in response to the nerve signal.

3. Less muscle activation

With reduced signalling, the selected muscle contracts less. This can reduce the repeated folding of the skin that contributes to expression lines. The visible change develops gradually rather than producing the immediate volume of a filler.

4. A temporary response

Communication between the nerve and muscle recovers over time. Movement gradually returns, and the timing of another treatment is assessed around your response rather than assumed from a fixed subscription.

Anatomy. Depth. Function.

Precision matters in every area.

An expression line is the visible sign of a deeper system. Your doctor considers the intended muscle, its depth and its neighbours, alongside the amount, concentration and volume delivered. A natural-looking result depends on preserving useful movement as well as softening a concern.

Forehead: brow support comes first

The frontalis lifts the eyebrows. Low forehead lines, a low resting brow or reliance on forehead movement to help open the eyes can call for a particularly restrained plan. Excessive weakening can produce brow heaviness or drooping. Skin laxity, underlying bone shape, age and previous surgery help explain why the same pattern or amount is not appropriate for every forehead.

Frown lines: depth and neighbouring structures

The corrugator and procerus work close to the brow and upper-eye structures. The target muscle changes depth along its course. Incorrect placement or unwanted spread can affect the muscle that lifts the upper eyelid and cause eyelid ptosis. Assessing the anatomy and selecting depth, amount and distribution carefully helps minimise that risk.

Crow’s feet: protect the cheek and smile

The orbicularis oculi helps close the eyelids, while nearby zygomatic muscles help elevate the cheeks and mouth corners. Treatment extending too low, too deeply or beyond the intended muscle can change cheek elevation or smile symmetry. A careful assessment considers the smile pattern, eyelid support, dry-eye symptoms and previous eye surgery.

Masseter: chewing function and smile balance

The masseter is a chewing muscle, with facial-expression muscles nearby. Our clinic favours a carefully mapped lower-masseter approach rather than treating high into the muscle routinely. Appropriate depth and placement, with a measured amount, help limit unwanted effects on nearby smile muscles. Muscle borders, chewing function, natural asymmetry and the support of the overlying skin are assessed together.

DAO and chin: small neighbouring muscles

The depressor anguli oris draws the mouth corner down, while the nearby depressor labii inferioris moves the lower lip. These muscles overlap closely. Unwanted spread during DAO or mentalis treatment can alter lower-lip movement and produce an uneven smile. An anatomical assessment, suitable depth and restrained delivery matter more than simply treating the visible shadow or dimple.

Lip flip and the upper-lip region

The orbicularis oris contributes to lip closure, speech, drinking and eating. Excessive weakening can affect these functions or look unnatural. We ask about activities that depend on precise lip control, discuss realistic goals and avoid assuming that more medicine will create a better lip shape.

Gummy smile: preserve a natural smile

Upper-lip elevators help reveal the teeth during smiling. Excessive reduction can lower the lip too much, reduce tooth display or alter smile symmetry. The cause of gum show, lip length, dental and skeletal features, and the pattern of muscle activity should be assessed before choosing an approach.

Nose: function as well as appearance

Nasal movement and upper-lip movement are closely related. Existing breathing difficulty, previous surgery and the support of the nasal tissues need assessment before considering a cosmetic muscle treatment. Unwanted effects on neighbouring muscles can alter lip elevation or expression; a muscle treatment cannot correct every structural nasal concern.

Neck and shoulders: retain useful strength

Neck and shoulder muscles have important support and movement functions. Treating the wrong layer or producing excessive weakness can affect comfort, head support or shoulder function. Neck treatment also needs attention to swallowing and nearby structures. Existing weakness, swallowing symptoms, posture and the proposed treatment purpose all influence suitability.

Excessive sweating: a different target

Acetylcholine also carries signals from nerves to eccrine sweat glands. For an appropriate local sweating treatment, botulinum toxin temporarily reduces release of this messenger near the glands, helping reduce sweat production rather than muscle movement. It does not remove the glands or cure an underlying medical cause.

Underarms and palms need different assessment. Palms can be sensitive, and unwanted effects on nearby muscles may affect pinch or grip. Your doctor considers skin thickness, the affected surface, hand function, previous response and alternatives. Product licences differ by area, so any proposed use outside its licence is explained before consent.

Experience and a measured approach

Choose a suitably qualified clinician who understands functional anatomy, explains their plan and provides follow-up. At consultation, ask how your movement was assessed, why a particular approach is recommended, and how an unexpected effect would be managed. Careful technique and a restrained plan reduce avoidable risk; they cannot make complications impossible.

Lower amounts do not guarantee that a side effect will be minor or resolve quickly. Recovery depends on the affected structure and individual response. More medicine is not a substitute for accurate assessment, and an unwanted effect should be reviewed rather than automatically treated with additional injections.

Your anatomy. Your response.

Why there is no single plan for every face.

Age and skin quality

Age is part of the history, not a dosing formula. A line visible only during expression differs from an established crease at rest. Elasticity, sun damage, hydration and tissue support affect how a line looks even when movement is reduced. Skin care, volume support or a separate skin-quality treatment may have a different role.

Strength, balance and previous treatment

Muscle size, natural asymmetry, brow position, previous surgery and earlier treatment response influence planning. Your doctor discusses the movement you want to retain. More medicine is not automatically a better result, and units from different products are not interchangeable.

OnsetChanges often begin within days; timing varies by product and area.
ReviewOur agreed muscle-directed plan includes a 14-day review; some effects continue developing beyond that visit.
DurationOften around three to four months for common upper-face uses; individual response varies.

Repeat treatment is not automatic. Your doctor follows the relevant product guidance and assesses function, response and suitable intervals.

Before. During. After.

Comfort, recovery and informed choices.

Your medical assessment

Tell the doctor about previous relaxer treatments, all medicines, allergies, pregnancy or breastfeeding, muscle or nerve conditions, eye symptoms and any swallowing or breathing difficulty. Infection at a proposed treatment site or certain medical conditions can make treatment unsuitable.

Comfort and everyday plans

Injections can cause brief stinging or discomfort. Small bumps, redness, tenderness or bruising may occur, so allow flexibility around an important event. You receive instructions appropriate to the treatment and know how to contact the clinic afterwards.

Risks and review

Possible effects include headache, unwanted weakness, asymmetry, brow or eyelid drooping and eye symptoms. These need individual advice rather than another injection automatically. At the included 14-day review, we assess the agreed muscle-directed plan; any adjustment is based on clinical suitability.

Seek immediate medical help for difficulty breathing, swallowing or speaking, or signs of a severe allergic reaction. Contact the clinic promptly for unexpected symptoms or concerns.

This is general educational information about a prescription treatment, not an individual recommendation. Product choice, indication, risks and expected response are discussed during medical assessment.

Explore your treatment options

Explore our relaxer treatment areas

The same medicine can have different purposes in different areas. These short introductions help you choose what to read next; each treatment page explains assessment, options, fees and care.

Anti-wrinkle treatment →

Assessment of forehead, frown and outer-eye lines, considering muscle movement, brow position and the skin changes visible at rest.

Masseter slimming and clenching →

For selected concerns involving bulky chewing muscles or clenching. Assessment considers jaw width, chewing function, facial support and possible dental causes.

Jawline lift →

A muscle-directed option for selected downward platysma pull around the jawline. It differs from adding filler, improving skin firmness or surgery.

DermoLift →

A superficial microdroplet relaxer approach considered for selected skin-texture and fine-line concerns. Its purpose and evidence differ from deeper muscle-directed treatment.

Nefertiti neck lift →

Assessment of platysma activity around the lower face and neck. Suitability depends on muscle pull, tissue support and preserving normal neck function.

Nose slimming →

For selected movement-related nasal concerns. Muscle activity is assessed separately from bone, cartilage and structural width; this does not replace rhinoplasty.

Shoulder slimming →

Assessment of trapezius muscle prominence and shoulder contour. Any muscle-directed plan must consider posture, everyday activity and preserving useful shoulder strength.

Calf slimming →

For selected calf prominence related to muscle bulk. Fat, swelling and muscle shape need different assessments, with walking and balance considered.

Bum lift consultation →

Explores whether a muscle-directed approach has a role in your concern. Evidence is limited; this does not add volume or reproduce surgery.

Excessive sweating treatment →

Assessment of troublesome sweating, its pattern and possible causes. Suitable treatment targets nerve signalling to sweat glands, rather than facial muscle movement.

Chin dimpling →

Considers mentalis activity behind a pebbled or dimpled chin. Assessment distinguishes muscle movement from a need for structural chin support.

Gummy smile →

For selected smiles where upper-lip muscle activity contributes to gum show. Dental, gum and skeletal causes may need different care.

Frown lines →

Focuses on the muscles between the brows, considering lines during expression and at rest, brow balance and nearby eyelid structures.

Crow’s feet →

Assesses outer-eye lines and orbicularis activity, while considering eye comfort, cheek elevation and the natural shape of your smile.

Bunny lines →

For selected lines appearing across the nose during expression. Nasal and upper-lip muscle relationships guide a restrained, individual assessment.

Forehead lines →

Considers frontalis activity and horizontal lines together with brow support. Existing lid heaviness or compensatory forehead movement can change the plan.

Your questions, clearly answered

Understanding relaxer treatments.

What is a relaxer treatment?

In this guide, relaxer means an injectable botulinum toxin type A medicine that temporarily reduces signalling from selected nerve endings to muscles. The exact product and its suitability are confirmed during medical assessment.

Does it fill a wrinkle?

Its main action is to reduce selected muscle activity. It does not add the structural volume of a dermal filler, and a line caused by skin damage or tissue loss may need a different approach.

Why is the result gradual?

The medicine acts within nerve endings, and the visible change develops over days rather than appearing as an immediate filling effect. Timing differs between products, areas and individuals.

Can I keep some facial movement?

Your doctor discusses the movement you want to retain and assesses muscle strength and brow or eyelid function. A personalised plan aims for balance; a completely motionless forehead is not a requirement.

Are all treatment areas and products equivalent?

No. Different muscles have different functions and risks. Product units are not interchangeable, and a medicine licensed for one indication is not automatically licensed for every facial or body area.

What if I have a concern afterwards?

Contact the clinic promptly about unexpected weakness, asymmetry or eye symptoms. Difficulty breathing, swallowing or speaking, or a severe allergic reaction, requires immediate medical help.

Manufacturer information & anatomical research

Where the explanation comes from.

We prioritised Allergan Aesthetics’ explanation of facial treatments, the manufacturer’s prescribing information and anatomical research. Product labels and approved uses differ between countries; the doctor confirms the information relevant to your treatment.

Read the source material

Information checked November 2026. Diagrams are original educational schematics.

BOTOX Cosmetic imagery © Allergan Aesthetics / AbbVie. Manufacturer science source. Brand illustration; this guide explains the treatment mechanism.