Botox for wrinkles: how it works, and where it goes

Botox is the most popular aesthetic treatment in the world, and it has one of the longest safety records in aesthetic medicine. It's also one of the most misunderstood. Here is what it actually is, how it works, where it goes on the face and how much is typically used.

What Botox is

"Botox" is the brand name of onabotulinumtoxinA, a purified protein made by the bacterium Clostridium botulinum. In tiny, measured doses, it blocks the signal (acetylcholine) that a nerve sends to tell a muscle to contract. The injected muscle relaxes, and the skin over it stops folding into a crease.

That's why Botox works on dynamic wrinkles, the lines that appear when you frown, squint or raise your eyebrows. It does much less for static lines that are etched in even when your face is at rest, or for sagging skin and lost volume, which need other treatments.

A short history

1. 1820sGerman physician Justinus Kerner describes food poisoning from spoiled sausages that paralyzes muscles but leaves the mind clear.
2. 1895Émile van Ermengem identifies the bacterium responsible.
3. 1970s–1980San Francisco ophthalmologist Alan Scott studies tiny doses to treat crossed eyes, first in primates and then in people.
4. 1989The FDA approves the toxin for crossed eyes (strabismus) and eyelid spasm (blepharospasm).
5. 1992Vancouver doctors Jean and Alastair Carruthers, an ophthalmologist and a dermatologist, publish the first report of using it to smooth frown lines.
6. 2002The FDA approves Botox Cosmetic for frown lines. Later approvals follow for crow's feet (2013), forehead lines (2017) and neck bands (2024).

Why we use it

• To soften expression lines between the brows, across the forehead and around the eyes.
• To prevent deepening. Relaxing a muscle that folds the skin thousands of times a day gives the skin a break, which is why many people start in their late 20s or 30s.
• For medical reasons too. Separate, larger-dose Botox products treat chronic migraine, heavy underarm sweating, overactive bladder and muscle spasticity.

The face map

Every face is different, but injectors work from a standard map of the muscles that cause each line. Hover over or tap a row to highlight that area. Green areas are FDA-approved for Botox Cosmetic; gold areas are common off-label uses that experienced injectors also treat.

1. 1
   Frown lines (glabella)Corrugator and procerus muscles. FDA label: 20 units over 5 sites. This is where most people start.
2. 2
   Forehead linesFrontalis muscle. FDA label: 20 units over 5 sites, given together with the frown lines (40 units total).
3. 3
   Crow's feetOrbicularis oculi muscle. FDA label: 24 units, 3 sites on each side.
4. 4
   Neck bandsPlatysma muscle. FDA label (2024): 26 to 36 units, depending on the number of bands.
5. 5
   Bunny linesNasalis muscle, the lines on the sides of the nose when you scrunch it. Off-label, small doses.
6. 6
   Lip lines and "lip flip"Orbicularis oris muscle. Off-label, very small doses.
7. 7
   Downturned mouth cornersDepressor anguli oris (DAO) muscle. Off-label.
8. 8
   Dimpled chinMentalis muscle. Off-label.
9. 9
   Jaw muscleMasseter, for teeth clenching or a slimmer jawline. Off-label, larger doses.

How many units?

Botox is measured in units of biological activity, not milliliters. The FDA-approved doses for Botox Cosmetic are:

A first full upper-face treatment (frown lines, forehead and crow's feet) is about 64 units on the label. In practice, doses are adjusted to the person: men often need more because their muscles are stronger, and people who want a softer, more natural look often get less, especially on the forehead.

Where most people start

The usual first treatment is the frown lines between the eyebrows, the "11s." It's the most studied area, the original FDA approval, and the lines people notice most. Forehead and crow's feet are often added at the same visit or at the next one.

The forehead is usually treated with the frown lines, not alone. The forehead muscle is the only one that lifts the brows, so relaxing it by itself can let the brows drop and feel heavy.

What to expect

Safety

At cosmetic doses, Botox has a strong safety record. The most common side effects are small bruises, a headache and, less often, a drooping eyelid or brow that wears off as the dose does. Serious problems are rare, but the label carries a warning that the toxin can spread beyond the injection area, which is one reason injection should be done only by a trained, licensed clinician using genuine product.

Botox isn't recommended during pregnancy or breastfeeding, or for people with neuromuscular conditions such as myasthenia gravis, or an infection at the injection site. Tell your injector about all your medicines, including blood thinners and recent antibiotics.

For the skin itself, Botox pairs well with a nightly retinoid and daily sunscreen. My note on tretinoin for anti-aging covers how to start.

Sources: BOTOX Cosmetic (onabotulinumtoxinA) prescribing information, dosage and administration. drugs.com. Carruthers JD, Carruthers JA. Treatment of glabellar frown lines with C. botulinum-A exotoxin. Journal of Dermatologic Surgery and Oncology. 1992;18(1):17–21. 20th anniversary and history of cosmetic botulinum toxin type A. MDedge Dermatology. 2022. mdedge.com.