In short. Two muscles run across the brow, so every contraction folds the skin the other way: why glabellar creases are vertical, and what that changes about treatment.
Key points
- A fold runs perpendicular to the pull.
- Vertical creases mean a muscle running across the brow; horizontal forehead lines mean a muscle running up it.
- The direction identifies the muscle responsible before anything is touched.
A crease forms at right angles to the muscle that makes it. That rule explains most of what is unusual about the lines between the brows: why they run up and down, and why the treatment that reaches them also changes the shape of the brow.
Two muscles, both running across the brow
The corrugator supercilii runs from the inner rim of the orbit outward to the skin above the middle of the brow. The procerus runs upward from the bridge of the nose, pulling the centre of the brow down. Both lie across the brow rather than along it, so when they shorten they gather the skin sideways, and skin gathered sideways folds the other way. The frontalis runs up the forehead instead, which is why its folds cross these.
Two patterns inside the same small area
The corrugator produces paired vertical columns above the inner brow. The procerus produces horizontal lines across the root of the nose and deepens the same creases from below. Most people have both in some proportion, and the proportion differs between them, so two faces with equally deep lines are not necessarily the same problem.
The direction is a signature
A fold runs perpendicular to the pull. Vertical creases mean a muscle running across the brow; horizontal forehead lines mean a muscle running up it. The direction identifies the muscle responsible before anything is touched.
Why this is the deepest folding point on the face
Skin between the brows is tethered to the bone by the structures around the brow fat pad, so it cannot slide away from a fold the way cheek skin can. The muscles there are thick and among the hardest working in the face, contracting in concentration, in bright light and in ordinary expression. A fold made thousands of times a day in skin tied down to bone becomes a groove rather than a passing wrinkle.
What the direction changes about treatment
Because the muscle is the moving part, the rung that reduces its pull is the one that reaches the mechanism. But the same muscles also hold the inner brow down, so quieting them changes the balance of the brow and the medial brow often rises. That change is sometimes wanted and sometimes not, which is why brow position is examined before treatment rather than after it.
Three things to check before treating
- Which muscle is producing the crease, and whether the pattern is corrugator, procerus or both.
- Whether the line is still visible with the face completely at rest, which is the part the muscle rung cannot reach.
- Where the medial brow sits now, because that is the position any change is measured against.
How that assessment is carried out is described in how frown lines are assessed. Why the etched part of the line behaves differently is covered in why these lines etch so deeply, and the way the brow responds to quieting the muscles has its own guide in the brow position trade-off.
Frequently asked questions
Why do the lines between the brows run up and down while forehead lines run across?
Because a fold always forms at right angles to the muscle producing it. The corrugator supercilii and the procerus both lie across the brow, so they gather the skin sideways and it folds vertically. The frontalis runs up the forehead, so its folds run horizontally. Two muscles a centimetre apart, pulling in directions ninety degrees apart, produce creases that cross each other.
Does the direction of the crease tell you which muscle is responsible?
It narrows it down. Paired vertical columns above the inner brow point to the corrugator, and horizontal lines across the root of the nose point to the procerus. Most faces show both in some proportion, and the proportion differs between people, so the direction identifies the candidates rather than settling the answer on its own.
Why are these lines deeper than lines elsewhere on the face?
Three reasons act together. The skin between the brows is tethered to the bone by the structures around the brow fat pad, so it cannot slide away from a fold the way cheek skin can. The muscles there are thick and work almost continuously. And the fold is made in the same place thousands of times a day, which turns a passing fold into a groove in the skin itself.
Risks & Limitations
- Relaxing the corrugator and the procerus also lifts the medial brow, and in a brow that already sits high that lift can become the complaint rather than the result.
- A drooping eyelid, double vision, or difficulty swallowing, speaking or breathing after an injection needs emergency care rather than a wait-and-see approach.
- Resurfacing carries a risk of pigment change and, rarely, of scarring, and its result is judged weeks after the last session rather than on the following morning.
- No rung removes a crease that is established in the skin. A line that is visible at rest usually softens, and any statement that promises more should be treated with suspicion.
When to Seek Care
- Difficulty breathing, chest pain, or difficulty swallowing or speaking after an injection needs emergency care immediately.
- A drooping eyelid, double vision, or an eye that will not close fully after treatment.
- Weakness or numbness on one side of the face, or a brow that has dropped on one side.
- A crease that has appeared or deepened over weeks rather than years, or any change in vision on one side.
References & Further Reading
- American Society of Plastic Surgeons (ASPS) — procedure and safety guidance
- National Institute for Health and Care Excellence (NICE, UK) — relevant guidance
- Cochrane Library — systematic reviews
- Chinese Medical Association Plastic Surgery Branch — clinical guidance
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.