What Is Botox and How Does It Work?

The short answer

Botox is the brand name of onabotulinumtoxinA, a prescription medicine made from botulinum toxin type A. A doctor injects very small amounts into chosen facial muscles. The toxin blocks the nerve signal that tells a muscle to contract, so the muscle moves less and the skin above it creases less. The change starts within days, settles over about two weeks and fades gradually over several months as the nerve endings recover.

What Botox actually is

Allergan, an AbbVie company, makes Botox. The US prescribing information for Botox Cosmetic (revised October 2024) calls it an acetylcholine release inhibitor and a neuromuscular blocking agent. For cosmetic use it lists four adult indications: moderate to severe frown lines between the eyebrows, crow’s feet, forehead lines and platysma bands in the neck.

Many people say “Botox” for every product of this type. The US Centers for Disease Control and Prevention (CDC) points out that Botox is a registered trademark and the name of the first FDA-approved cosmetic botulinum toxin product, and that other approved products exist. Dysport is one of them. The products are not interchangeable on paper: the label states that Botox units cannot be compared with, or converted into, units of any other toxin product.

Botulinum toxin is a prescription-only product. The CDC notes that only people with a valid healthcare license can buy it, and that injections should come from a trained, licensed provider. If you want to see how a doctor plans this treatment in practice, the page on doctor-led botulinum therapy at the clinic describes the assessment and the zones.

How Botox works inside the muscle

A muscle contracts when its nerve releases a chemical messenger called acetylcholine at the point where nerve and muscle meet. According to the prescribing information, Botox binds to acceptor sites on the motor nerve ending, enters it and stops the release of acetylcholine. It does this by cutting SNAP-25, a protein the nerve ending needs to dock and release acetylcholine from its vesicles.

The result is partial chemical denervation: a local reduction in the activity of the injected muscle. The label adds that the muscle may atrophy, that the nerve may sprout new endings, and that there is evidence of reinnervation, which slowly reverses the effect. This recovery is why the treatment is temporary.

Expression lines form where a muscle repeatedly folds the skin. The label ties each approved indication to a specific muscle:

Botox acts on the muscle and its nerve supply. It does not replace lost volume or change skin texture, which is why doctors often discuss it next to other treatments when several concerns overlap. Our overview of wrinkle treatment options shows where botulinum toxin fits among them. Some zones, such as the masseter or a gummy smile, are treated with botulinum toxin outside its official indications, and a doctor should tell you so before you decide.

The prescribing information also notes that, with current analytical technology, Botox Cosmetic cannot be detected in the blood after intramuscular injection at the recommended doses.

How a treatment session goes

1. Consultation. The doctor studies how your face moves, how strong the muscles are and whether one side differs from the other. You report your medical history and current medicines. The Medication Guide asks patients to mention muscle or nerve diseases such as myasthenia gravis, allergy to any toxin product, swallowing or breathing problems, bleeding problems, planned surgery, drooping eyelids, pregnancy or breastfeeding, any other toxin injection in the last four months, and medicines such as muscle relaxants, blood thinners or injected antibiotics.
2. Preparation. The skin is cleansed and the injection points are mapped. A 2016 international consensus (Global Aesthetics Consensus Group) recommends removing all makeup, cleansing the skin and using a sterile technique.
3. Injection. The label describes a fine 30 to 33 gauge needle and small measured volumes placed into the muscle. Per the clinic’s treatment page, most sessions take 10 to 20 minutes, most patients tolerate the injections well, and a numbing cream can be applied on request.
4. Review. Because the effect builds over days, the doctor can check the result after about two weeks and adjust the plan if a muscle needs more.

The hours after the injection have their own short list of dos and don’ts. We cover them in Botox aftercare: what to do and what to avoid.

When you notice the change and how long it lasts

For frown lines, the prescribing information says the initial doses typically cause chemical denervation one to two days after injection, with the effect increasing through the first week. It gives the duration of effect for frown lines as approximately three to four months. The clinic’s treatment page describes the full result as settling over about two weeks.

Timing varies with the zone, the dose and your individual response, which is one reason the exact plan belongs to your doctor. The label also states that the safety and effectiveness of dosing more often than every three months have not been clinically evaluated, so repeat treatments follow a spacing your doctor sets.

Who should not have Botox and what can go wrong

The label lists two contraindications: known hypersensitivity to any botulinum toxin product or to an ingredient in the formulation, and infection at the planned injection site. It also advises caution in people with a neuromuscular disorder, because the disease may worsen the effect of the treatment. The Medication Guide says Botox Cosmetic is not recommended for people under 18, and it says it is not known whether the product can harm an unborn baby or pass into breast milk.

The most common adverse reactions in the clinical trials summarised in the label were eyelid ptosis (3%) for frown lines, eyelid edema (1%) for crow’s feet, and headache (9%) and brow ptosis (2%) for forehead lines. The clinic’s treatment page also lists injection marks, swelling and bruising. The clinic’s treatment page describes a drooping eyelid or brow as temporary, passing as the product wears off. The label also gives specific steps to reduce ptosis, such as keeping injections away from the muscle that lifts the upper eyelid and at least 1 cm above the central eyebrow.

Your doctor decides whether the treatment suits you after an in-person assessment, and your doctor gives the exact instructions for your case.