In short. Expression lines are lines produced by muscle contraction, and relaxing the muscle reduces the folding that creates them. Faint lines often soften substantially, while established creases soften only at the movement component, and the face moves less in the treated area.

Key points

  • Relaxing a muscle reduces the folding that produces a line; it does not erase the line.
  • Faint lines often soften substantially; established creases soften only at the movement component.
  • Several muscles sharing one line produce a partial change when one is relaxed.
  • Weakening the wrong muscle near the brow or eyelid can cause a droop.
  • Relaxing a muscle does not restore volume, lift descended tissue, or remove a formed crease.

What relaxing the muscle does to a line

The muscle-relaxing injectable is most predictable where a line is produced by one identifiable muscle group, and where that muscle can be relaxed without affecting a structure the patient needs. Understanding that is more useful than a list of areas, because it explains why some lines soften convincingly and others only partly.

It reduces contraction of the muscle it is placed into. The skin above that muscle is then folded less often and less forcefully, so a crease produced by folding becomes shallower and less likely to deepen further.

How long does the change take to appear?

The change appears over days and settles over a week or two, which means the result is judged after that period and not on the first evening.

What the result is, and is not

The change is a reduction, not a disappearance. Faint lines often soften substantially; established creases soften at the movement component and retain what the skin itself has become. The face also moves less in the treated area, which is the mechanism and is visible, and how much movement remains is a matter of how much is used and how the individual responds.

Where one muscle shares a line with others

Where a single muscle is responsible, relaxing it changes the line along its whole length. Where several muscles contribute to the same line, relaxing one of them produces a partial change, and the clinician has to decide whether treating the others is worth the effect it would have on expression.

Where the margin narrows

The anatomy around the target is the main part of the assessment. The muscles that raise the brow and the muscle that raises the eyelid sit close to the areas commonly treated, and weakening the wrong one produces a brow or eyelid droop, or a brow that sits differently on the two sides. These effects are recognised, they are usually temporary, and they resolve as the treatment fades. Their likelihood depends on the anatomy, the placement and the amount used, which is why an injector's familiarity with the region matters more than the substance does.

Line or finding What produces it What relaxing the muscle does What it does not do
A line from one identifiable muscle group One muscle Changes the line along its whole length Remove what the skin has already formed
A line from several muscles More than one muscle contributing Produces a partial change Change the line along its whole length
A line near the brow or eyelid Muscles close to the structures that raise the brow and the eyelid Reduces contraction, with a narrower margin for error Leave the brow and eyelid position unaffected
Hollow temple or flattened cheek Lost volume Nothing Restore volume
Brow that has dropped with age Descended tissue Nothing, because weakening the muscle that pulls it down does not raise it Lift descended tissue
A crease the skin has already formed Skin that has changed, not movement alone Softens the movement component Remove the established component

What relaxing a muscle will not do

  • Restore volume. A hollow temple or a flattened cheek is unchanged by reducing movement over it.
  • Lift descended tissue. The brow that has dropped with age is not raised by weakening the muscle that pulls it down.
  • Remove a crease that the skin has already formed. Part of the line is no longer produced by movement.

Why does the assessment decide the plan?

The treatment is chosen because a specific muscle is producing a specific line, and the assessment is the part that establishes it. A clinic that offers it for every line on a face is describing a routine rather than your anatomy.

Sources

Internal links

Frequently asked questions

Which expression lines respond most predictably?

Lines produced by a single, identifiable muscle group that is well separated from the muscles that control the eyelid and brow. The horizontal lines across the forehead and the lines between the brows are the classic examples. The fine lines around the eyes respond too, but the muscle there borders structures that matter, so the margin for error is narrower.

Why do some lines only partly soften?

Because part of the line is no longer produced by movement. A crease that has been folded thousands of times leaves a mark in the skin itself, and reducing the folding does not erase what the skin has already become. The movement component softens; the established component remains, and that is why a plan sometimes combines relaxing the muscle with treating the skin surface separately.

Do the lines come back worse if I stop?

They return to what they would have been, which is not the same as worse. When the effect fades, the muscle resumes its previous activity and the lines reappear at the depth they had reached. The impression of worsening comes from comparing the treated face with the untreated one after a period of treatment, not from the treatment making the underlying process more aggressive.

Risks & Limitations

  • Bruising and swelling after either treatment; with filler, swelling can be marked for several days and changes the shape of the area until it settles.
  • Weakening of a neighbouring muscle after a muscle-relaxing injectable, producing a brow or eyelid droop or an asymmetry between the two sides.
  • Lumps, irregularity or an unnatural contour after filler, which can appear immediately or become visible later as the material settles.
  • Vascular occlusion after filler — material obstructing a blood vessel, which threatens the tissue it supplies and is a medical emergency.
  • Delayed reactions, nodules and infection after filler, sometimes appearing well after treatment.
  • Both treatments are temporary and both are repeated. Neither stops the muscle from moving or the face from continuing to change.
  • Muscle relaxation has no reversal agent and has to be waited out; a dissolvable gel filler can be partly broken down with an enzyme, but not every material can.
  • No outcome is guaranteed, and individual response varies with the area, the anatomy and the material used.

When to Seek Care

  • Sudden severe pain after filler, or skin that turns white, dusky or mottled — contact the treating team the same day.
  • Any change in vision after an injection on the face — seek emergency care immediately.
  • Fever, spreading redness, or a painful swelling that is worsening rather than settling.
  • A lump that is increasing, or skin breakdown over an area that has been injected.
  • Difficulty breathing, or swelling of the lips, tongue or throat — seek emergency care immediately.
  • A droop or asymmetry that is not improving as the treatment fades, for review and possible adjustment.

References & Further Reading

  • American Society of Plastic Surgeons (ASPS) — injectable and dermal filler safety guidance
  • National Institute for Health and Care Excellence (NICE, UK) — relevant guidance on non-surgical cosmetic procedures
  • Cochrane Library — systematic reviews in injectable facial aesthetics
  • Chinese Medical Association Plastic Surgery Branch — clinical guidance

Medically reviewed by Ke He, MD (何锞), Deputy Director & Head of Skin & Laser Aesthetics. Last reviewed: 19 September 2026.

This page is patient education, not medical advice, and it does not cite individual studies. Discuss your own case with a qualified clinician. To arrange an assessment at Chongqing West District Hospital, see Contact & Consultation.