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How to Recognise and Correct Rainbow Lines After Botulinum Toxin Treatment

Jan 5
Rainbow lines — sometimes referred to as “wifi lines” — are curved accessory forehead lines that may appear following Botulinum Toxin treatment to the frontalis muscle. Although they are not harmful, they can be aesthetically undesirable and are usually a sign of uneven muscle weakening across the forehead.

Understanding why rainbow lines occur — and how they can be safely corrected — is an important part of advanced toxin practice and post-treatment complication management.

This article explains what causes rainbow lines, how to recognise them clinically, and the recommended principles for safe correction.

What are Rainbow Lines

Rainbow lines are curved horizontal lines that appear in the upper forehead, above the treated area of the frontalis. They typically develop when:
 • the lower and central fibres of the frontalis are weakened by toxin
 • the upper frontalis fibres remain active
 • residual muscle movement occurs above the treatment zone

Because the remaining active fibres continue to contract, they create a secondary arc of movement, which presents as curved accessory forehead lines.

Clients often notice them most:
 • when raising the eyebrows
 • during facial expression
 • in bright light or photographs

Rainbow lines tend to be more common when:
 • toxin is placed only in the lower forehead
 • dosing is uneven across the frontalis
 • natural brow position is higher
 • the client has thin soft tissue

They are best prevented through balanced dosing across the full forehead, taking into account muscle height, brow position and natural expression.

Why do Rainbow Lines Appear?

The frontalis muscle is unique because it is: vertically oriented responsible for eyebrow elevation the only elevator muscle in the upper face If the lower fibres are softened but the upper fibres remain untreated, the muscle can recruit movement in the remaining active area.
This results in:
 ✔ overactivity in the untreated upper frontalis
✔ accessory line formation
✔ a curved “rainbow-like” contour
This is not a treatment “error” — rather, it reflects: anatomical variation dosing strategy the patient’s natural movement pattern Recognising the mechanism behind rainbow lines helps inform safe and appropriate correction.  

Correcting Rainbow Lines

In most cases rainbow lines can be improved with a small, conservative top-up dose in the upper forehead.
The aim is to:
 • gently soften the remaining active fibres
 • maintain brow stability and support
 • avoid excessive heaviness or brow ptosis

This is achieved using a light-dose, minimal-point approach.

Typical Correction Approach (Principles)
A common correction technique involves:
 • very light dosing
 • superficial placement
 • injections placed along the arc of the visible accessory line

Typical clinical approach may include:
 • around 0.5 units per point
 • minimal injection points
 • careful anatomical assessment before treatment
This allows movement to be balanced without over-relaxing the frontalis.

Safety Considerations

Because the frontalis contributes to eyebrow elevation, correction must be carried out cautiously.

Key precautions include:
 • Avoid high doses in the upper forehead (risk of brow heaviness)
 • Keep injections at least 2 cm above the brow
 • Assess natural eyebrow position before treating
 • Use minimal units and review after 2 weeks
 • Avoid treating close to the brow tail in clients with naturally low brows

The goal is always:

✔ improve the accessory lines
✔ retain natural expression
✔ maintain brow support

Rainbow line correction is a refinement technique, not a full retreatment.

When to Review or Reassess

A follow-up review is important where:
 • results appear asymmetric
 • brow heaviness is reported
 • lines do not improve as expected
 • the client has strong frontalis recruitment patterns

Some clients may benefit from dose mapping on subsequent treatments, ensuring more even coverage across the frontalis.

This forms part of progressive treatment planning and aesthetic outcome optimisation.

Key Takeaways for Practitioners
 • Rainbow lines develop due to residual contraction in untreated upper frontalis fibres
 • They are typically caused by uneven muscle weakening after toxin treatment
 • They can usually be improved by light top-up dosing in the accessory line area
 • Treatment must remain conservative to avoid brow ptosis
 • Anatomical assessment and brow position should guide technique

Understanding movement patterns and muscle dynamics is essential for safe toxin practice and high-quality aesthetic results.

Continue Developing Your Clinical Knowledge

If you found this helpful, you may also be interested in:

✔ facial anatomy education
✔ complication recognition and management
✔ advanced toxin treatment planning

We provide accredited online practitioner training designed to support safe, evidence-based aesthetic practice and clinical confidence.