What is Botox? Understanding botulinum toxin

"Botox" has become the everyday word for botulinum toxin, the way some product names end up standing for a whole category. Behind the word are in fact several medicines, all injected into a muscle to reduce its contraction for a limited time. This page brings together the essentials: what the toxin is, how it works, how long it takes to act and how long it lasts, which areas it is approved for, its risks and the precautions to know about. Each point links to a more detailed page and to the official sources.

What is botulinum toxin?

Botulinum toxin is a protein produced by bacteria of the genus Clostridium, including Clostridium botulinum³. It is the cause of botulism, a serious form of poisoning: botulinum toxins are among the most potent poisons known³. Purified and used in very small doses, in a specific muscle, it becomes a medicine used in neurology, urology, pain management and aesthetic medicine³.

In practice, it is a medicine in its own right, with a marketing authorisation, an official label and strict rules of use. In France, the first authorisation of a botulinum toxin for aesthetic use dates from 2003⁴. The toxin is injected by a doctor, with a fine needle, directly into the muscle or muscles responsible for an expression line.

The principle is simple: it does not act on the skin itself but on the muscle beneath it. When the muscle contracts less, the skin over it creases less, and the line caused by that movement softens. This is why botulinum toxin works on expression lines (the ones that deepen when you frown or smile), not on sagging skin or loss of volume.

"Botox" or "botulinum toxin": what are we talking about?

"Botox" is the word most people use for the whole family of botulinum toxins. On this site, we use it in titles because it is the word you search for, and we write "botulinum toxin" in the text, because it is the accurate term and it covers several medicines.

Several botulinum toxins are approved for aesthetic use in France⁴. All belong to type A, except one, more recent, of serotype E, approved in the European Union since 15 July 2026⁵. As of 9 October 2026, it is also approved in Canada (since 22 June 2026)¹¹. These products are not strictly identical: each has its own label, its own indications, its own age limits and its own dosing unit. All the labels state that the units of one toxin are not interchangeable with those of another^2,7. A dose expressed for one product therefore says nothing about the dose needed with another: choosing the product and the dose is the doctor’s job.

How does botulinum toxin work?

To contract, a muscle receives an order from the nerve that controls it. This order is carried by a chemical messenger, acetylcholine, released by the nerve ending where it meets the muscle. Botulinum toxin blocks this release^1,2.

The labels describe the steps: after injection, the toxin binds to receptors on the surface of nerve endings, enters the nerve ending, and its active part then cuts a protein essential for releasing acetylcholine, called SNAP-25^1,2. Without acetylcholine, the muscle no longer receives the signal and relaxes, partially and temporarily. The mechanism is explained step by step, in plain language, on our page on the mechanism of botulinum toxin in the muscle.

This mechanism also explains two important features. First, the toxin does not act instantly: it needs time to go through these steps. Second, its effect is reversible: the nerve ending eventually recovers its ability to release acetylcholine^1,9.

How long does it take to work, and how long does it last?

Timings depend on the family of toxin:

• Long-acting toxin (type A): first effects usually appear within 2–3 days, at the latest within about a week, and the peak effect is reached between week 2 and week 4 depending on the product^1,7. The effect usually lasts 3–4 months, and up to 6 months for some products^1,10.
• Short-acting toxin (serotype E): first effects appear from 8 hours after the injection, the effect peaks around day 7 and usually lasts 2–3 weeks².

Two pieces of advice follow from these figures. Do not judge a result before the peak effect: an asymmetry or an effect that seems too weak in the first days may still change. And keep in mind that onset and duration go hand in hand: the toxin that works fastest is also the one that lasts the shortest time.

To go further, the page on when botulinum toxin starts to work details first effects and peak effect, and the page on the duration of botulinum toxin and why it wears off explains why the effect fades and how often sessions can be repeated.

Which areas is botulinum toxin approved for?

In France, aesthetic use of botulinum toxin is approved for a small number of areas, always in adults and when the lines have a significant psychological impact^1,2:

• frown lines (between the eyebrows), for every toxin approved for aesthetic use, including the short-acting toxin^1,2,7;
• crow’s feet, for some type A toxins^1,7;
• forehead lines, for some type A toxins^1,6.

Other areas are treated in practice (eyebrows, nose, gummy smile, lips, chin, jaw, neck), but they do not appear in any aesthetic approval in France: this is off-label use, which should be presented as such and discussed with your doctor. Our botulinum toxin guide to the 11 areas of the face explains, for each area, why it is treated, what is approved and what to know beforehand.

Two families: long-acting and short-acting toxins

For more than twenty years, every toxin used for aesthetic purposes in France was type A⁴. Since July 2026, a short-acting botulinum toxin has been approved in the European Union, for a single indication: frown lines in adults^2,5.

Both families work the same way, by cutting the SNAP-25 protein^2,3. They differ in their profile: one works faster and for a shorter time, the other more slowly and for longer. Neither is better than the other; the short-acting toxin adds a choice, to be made with your doctor. Its label specifies that it should be used occasionally².

The facts about this new generation (approval, studies, a neutral comparison with the long-acting toxin, and situations where the latter remains the right choice) are gathered on our page about the new botulinum toxin, without ranking the two families.

Is Botox dangerous?

It is a fair question for a product derived from a poison. The answer lies in the dose and in how it is used: the labels set out precisely the doses, the injection points and how often sessions can take place, and remind doctors that the recommended dose must not be exceeded¹.

The side effects described in the labels usually occur in the first days after the injection, are transient and most often mild to moderate¹. Among the most common are injection-site reactions (pain, bruising, swelling, redness), headache and, depending on the area, a drooping eyelid or eyebrow¹. These last effects result from the toxin acting on a neighbouring muscle and are temporary.

More serious effects are very rarely reported: spread of the effect away from the injection site, with muscle weakness, swallowing, speech or breathing problems and, exceptionally, a severe allergic reaction^1,2. The labels ask patients to seek immediate medical care if they have difficulty swallowing, speaking or breathing¹. In that situation, call emergency services straight away (15 or 112 in France, or your local emergency number).

A "frozen" look is not an inevitable effect of the toxin: the strength of the effect depends on the dose and on the muscles chosen by the doctor. If a result worries you after an injection, our help pages for a disappointing or worrying result help you identify the problem, how long it may last and when to see a doctor.

What precautions before and after an injection?

Botulinum toxin is not suitable for everyone. It is contraindicated in case of allergy to one of its components, a generalised neuromuscular disease such as myasthenia gravis, or infection at the injection site^1,2. It is not recommended during pregnancy and breastfeeding^1,2, nor under the age of 18¹. Some treatments, notably anticoagulants and certain antibiotics, must be mentioned to the doctor^1,6.

It is just as important to mention a recent toxin injection, whatever the product: excessive muscle weakness may be made worse by another toxin injected before the effects of the previous one have worn off¹. The full list, and the advice for after the injection, is on our page on what to check before and after a botulinum toxin injection. Never change a treatment on your own before an injection: ask the doctor who prescribed it.

What the science says

Research on botulinum toxins is very active. Seven serotypes are traditionally distinguished, labelled A to G, and they do not all cut the same protein³. Types A and E both cut SNAP-25, but not at the same place, and the active part of the type A toxin persists much longer in the nerve ending than that of the type E toxin³. This largely explains their different durations of action.

Science also sheds light on antibodies: they are rare, and high doses and closely spaced injections make them more likely⁸. In the trials of the short-acting toxin, no patient developed neutralising antibodies, but data are still limited². These topics, along with nerve recovery and spread of the toxin, are explained on our page on the science behind botulinum toxins.

The questions people ask most

Does your face necessarily freeze? Can you become resistant? What happens when you stop? Can a badly placed toxin be "removed"? These questions come up again and again, and the answers that circulate are sometimes wrong. We answer them one by one, with sources, on our page of common questions and myths about botulinum toxin.

One point about reversibility deserves to be made clear: once the toxin has entered the nerve ending, it can no longer be reached by the antibodies that could neutralise it³. In practice, an unwanted effect fades over time, as the nerve recovers⁹.

Is it right for me?

No web page can answer this for you. The decision rests on an examination: the type of lines, whether they appear only with movement, your expectations, your medical history, your treatments and your age. Data are limited after 65 for several toxins, type A as well as serotype E^1,2,6. Some lines, especially those visible at rest, may not respond fully to the toxin alone.

This site gives you what you need to prepare that conversation: ask your questions, ask which product is planned, for which area, whether that area is part of the approval, and which side effects are possible. This is to be assessed with your doctor.