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.
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.
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.
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.
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.
