Key takeaways
- Forehead Botox works well on lines that appear when you raise your brows; deep lines that stay at rest are sometimes treated with other procedures as well.
- How it works: The forehead muscle folds the skin again and again, and Botox reduces that muscle's movement so the skin creases with less force.
- Onset and duration: Changes usually start within a few days, and the effect typically lasts about three to four months.
- What to watch: The forehead muscle is the one that lifts your brows, so the brows can feel heavy or look lower; that's why brow height and frown movement are checked together.
What Botox can do for horizontal forehead lines depends on whether they show up when you raise your eyebrows or stay etched in even when your face is relaxed. Many people see three or four lines when they lift their brows in the mirror, and one faint line that doesn't fully disappear when they let go. That line tends to be the first thing they notice in photos, so they ask whether Botox will smooth all of it.
This article explains how forehead lines form, how to tell lines that appear with movement from lines that stay at rest, what a clinical trial showed about results and risks such as a lowered brow, and what's worth knowing before a consultation.
Why do horizontal forehead lines form, and where does Botox act?
Why do horizontal forehead lines form, and where does Botox act?
Horizontal forehead lines form when the frontalis, the muscle that lifts your eyebrows, contracts and folds the skin crosswise. It's the same movement your brows make when you're surprised or worried, which is why they're often called "worry lines." When the same spot folds thousands of times over the years, a line that once showed up with movement alone gradually stays even when you relax.
Botox (botulinum toxin) blocks the release of acetylcholine, the chemical messenger that carries the "move" signal from nerve endings to the muscle. With a weaker signal, the muscle contracts less and the skin above it folds less. It doesn't fill or tighten the skin itself; it reduces muscle movement, and that's the starting point for everything in this article.
So the lines Botox responds to best are the ones made by muscle movement. Creases that have already settled into the skin because it has thinned and lost elasticity won't vanish right away just because movement is reduced. A single forehead often has both types, so it helps to work out which one is larger first.
Frontalis: a thin muscle covering the forehead; when it contracts, the brows rise and horizontal lines form.
Lines with movement or lines at rest: which kind are yours?
Lines with movement or lines at rest: which kind are yours?
Forehead lines can be sorted into two groups by when you see them. With a mirror, you can get a rough idea at home.
| Type | When you see it | What Botox can be expected to do |
|---|---|---|
| Lines with movement | Appear when you raise your brows and disappear when you relax | Less folding force, so lines form less |
| Lines at rest | Stay etched in even with a relaxed face | May soften, but other procedures are sometimes considered too |
| Mixed | Fade when you relax, but one or two lines remain | Movement is reduced and the remaining crease is assessed separately |
Raise your eyebrows as high as you can in the mirror, then let your forehead go completely slack. If the lines almost disappear, lines with movement make up most of what you see. If they stay clearly visible, lines at rest have already set in. It also helps to notice whether you habitually tense your forehead when you open your eyes wide, since that's useful to mention at a consultation.
Lines with movement or lines at rest: which kind are yours?
How much did lines improve in research, and what should you watch for?
How much did lines improve in research, and what should you watch for?
In a phase 3 clinical trial of 787 people with moderate or more severe forehead lines, Botox was injected into both the forehead and the frown area between the brows. At day 30, a two-grade or greater improvement was seen in 45.6% of the 40-unit group and 53.0% of the 64-unit group, compared with 0.6% of the placebo group. That means roughly half improved by two grades or more, not that everyone's lines were fully smoothed. The study was sponsored by the manufacturer and enrolled people with moderate or more severe lines.
How much did lines improve in research, and what should you watch for?
The U.S. Food and Drug Administration (FDA) label also specifies that forehead lines are treated together with frown lines, and lists headache at 9% and brow drop (eyebrow ptosis) at 2% as the most common side effects in forehead line trials. Because the frontalis is the main muscle that lifts the brows, weakening it alone can make the brows sit lower or feel heavy. Weakness spreading to nearby muscles is reported in fewer than 10% of treatments, and if it happens, it can last up to 12 weeks.
It's also useful to know when results appear and how long they last. The muscle usually starts to relax within two to four days, the effect is most noticeable around day 10, most people see a change within a week, and it lasts about three to four months. Pain, bruising, swelling and redness at the injection site are the most common reactions, and bruising is more likely if you take blood-thinning medication.
How STON Clinic approaches forehead line Botox
How STON Clinic approaches forehead line Botox
STON Clinic explains forehead lines this way. Forehead lines form as the forehead muscle folds the skin again and again when you raise your eyebrows. Botox reduces that muscle's movement, so the skin creases with less force and lines form less. It works well on lines that appear with movement, and deep lines that stay at rest are sometimes treated with other procedures as well.
That's why the consultation looks at your forehead both with brows raised and at rest, along with your usual brow height and frown movement. Botox should be avoided if you have a condition that weakens muscles (such as myasthenia gravis), an infection at the injection site, a past allergy to botulinum toxin, or if you're pregnant or breastfeeding. Some antibiotics (aminoglycosides) can strengthen its effect, so let the clinic know about any medication you're taking.
If any of the following symptoms appear after treatment, don't wait; get medical care right away. Rarely, the toxin's effect can spread beyond the injection site, and this can show up hours to weeks later.
- Trouble swallowing or breathing
- Slurred speech or double vision
- Eyelids drooping so much it's hard to keep your eyes open
At a consultation, starting with "Are my forehead lines mostly lines with movement or lines at rest?" makes the plan easier to understand. When you contact the clinic, include two front-facing photos, one with your brows raised and one relaxed, along with when and where you last had Botox and any medication you're taking.
If this raised a question about your own skin
Ask a questionReferences
- How botulinum toxin works, how long it lasts and side effects — DermNet, 2020 — DermNet NZ
- Botulinum toxin overview — American Academy of Dermatology — American Academy of Dermatology
- Phase 3 trial of Botox in the forehead and frown area — Dermatol Surg, 2018 — PubMed Central
- BOTOX Cosmetic prescribing information — U.S. Food and Drug Administration (FDA), 2024 — U.S. Food and Drug Administration
Frequently asked questions
Q. Why does Botox smooth forehead lines?
A. Forehead lines form as the forehead muscle folds the skin repeatedly when you raise your brows. Botox reduces that muscle's movement, so the skin creases with less force and lines form less. Because it works by reducing movement, it suits lines that appear when you move.
Q. Will Botox remove deep lines I can see even at rest?
A. They can soften as movement decreases, but creases that have already set in won't disappear right away. Deep lines that stay at rest are sometimes treated with other procedures as well. Which type is larger is judged at an exam by comparing your forehead with and without expression.
Q. When do results show, and how long do they last?
A. DermNet reports that the muscle starts to relax within two to four days and the effect peaks around day 10. The American Academy of Dermatology says most people see results within three to seven days, lasting about three to four months. Duration varies because muscle strength differs from person to person.
Q. Can forehead Botox make my eyebrows droop?
A. Yes, it can. The forehead muscle lifts the brows, so when it's weakened, the brows can drop or feel heavy. The FDA label lists brow drop at 2% in forehead line trials, which is why your usual brow height and forehead habits are checked before treatment.
Q. Why is the frown area treated along with the forehead?
A. The FDA label specifies that forehead lines are treated together with frown lines. The forehead muscle lifts the brows while the frown muscles pull them down, so weakening one side alone can shift that balance. Exactly where to inject is decided after looking at how your face moves.
Q. Can I get a headache afterward?
A. The FDA label lists headache at 9% as the most common side effect in forehead line trials. DermNet notes that a mild headache can appear two to four hours after injection and usually responds to ordinary pain relievers. If the headache keeps getting worse or comes with other symptoms, please get medical care.
Q. Who shouldn't get Botox?
A. It should be avoided if you have a condition that weakens muscles, an infection at the injection site, a past allergy to botulinum toxin, or if you're pregnant or breastfeeding. Some antibiotics can strengthen its effect. Be sure to tell the clinic about your medications and health conditions before the consultation.
Q. Does getting it more often make it last longer?
A. DermNet advises against intervals shorter than 8 to 12 weeks to lower the risk of developing antibodies. It also notes that with repeated treatment, the muscle can gradually thin and the interval may lengthen. The timing of your next session is set by how the effect wears off.
Jangju Kim Senior Director
JANGJU KIM
Dr. Jangju Kim is a clinic director at STON Clinic, LOTTE HOTEL in Myeongdong.
Career / Education
- 현) 스톤클리닉 명동 롯데호텔 원장
- 경희대학교 의과대학 졸업
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