Botox: botulinum toxin injections for expression lines, how they work, how long they last and what the risks are

On this page you will find general medical information about botulinum toxin injections for expression lines: how the treatment works, what studies show about effectiveness and duration, and which risks are important to know before deciding. If you are also interested in injections of fillers (hyaluronic acid, calcium hydroxylapatite), a completely different treatment intended for a different problem, you can read about them separately.

What is botulinum toxin type A, and how does it smooth lines?

Botulinum toxin type A is a medicine that temporarily blocks the signal from nerve to muscle, and so relaxes the injected muscle. Expression lines, such as the vertical line between the brows or "crow's feet" at the sides of the eyes, form from repeated contraction of small facial muscles over the years. When the muscle that creates the line is more relaxed, the skin above it creases less with movement, and the line smooths out.

By area: forehead lines, frown lines between the brows and lines around the eyes: each area has its own page with the causes, research and risks specific to it. An overview of all injection points on the face and neck, from the temples to the masseter muscle, is in the guide to Botox injection points. A completely separate use, unrelated to wrinkles, is injection into the chewing (masseter) muscle to slim a square jawline; see botulinum toxin for the masseter muscle.

The international consensus on the subject stresses an important term: the goal is "modulation" of muscle movement, not complete paralysis, especially in the upper forehead, in order to preserve natural facial movement¹. The treatment is mainly suitable when the main cause of the line is active muscle contraction, not a line that has already become "set" in the skin even at rest, and not sagging tissue. In Israel botulinum toxin is classified as a prescription medicine, not as a medical device like fillers⁵.

Three botulinum toxin type A products are registered in Israel. The active substance in all three is the same, but their units are not interchangeable, and one of them contains no complexing proteins. In head-to-head trials in frown lines, two of the products gave similar results and duration of effect, and claims that one product "spreads" more than another are not well supported. Details on the page types of botulinum toxin and the differences between them.

Which lines respond to treatment, and which do not?

The treatment is intended for expression lines created by muscle movement, not for permanent lines that remain even when the face is at rest. In Israel the registered aesthetic indications in the product leaflets are frown lines between the brows, lines at the sides of the eyes ("crow's feet"), and for some products also horizontal forehead lines, in adults when the lines have a psychological impact on the patient².

Besides the forehead, the area between the brows and around the eyes, botulinum toxin is also used for more targeted areas, such as bunny lines on the bridge of the nose and a gummy smile.

Deep lines that remain without movement, loss of volume in the cheeks or chin, and sagging skin are a different kind of problem, and treatments such as fillers, collagen stimulators (biostimulators) or a face lift with dissolvable threads are sometimes suitable for them. Several types of treatment are sometimes combined in the same area of the face, but the decision about which combination is suitable is made at a personal examination.

How effective is the treatment, according to studies?

In controlled studies, most patients reported a marked improvement in lines compared with placebo. A 2021 Cochrane review, which included 65 controlled trials and 14,919 participants, found that the treatment reduces expression lines within 4 weeks, with high to moderate certainty of evidence³.

For frown lines between the brows specifically, the chance of a result the patient perceived as a "success" was significantly higher than with placebo at week 4 after treatment, with moderate to high certainty³. The review also found no difference in effectiveness between the different registered products that were compared directly, at the doses tested; in other words, there is no evidence that one product is "better" than another³.

How soon do you see a result, and how long does it last?

The first result is usually seen within 3–7 days, and the full effect settles within about two weeks. This is according to the American Academy of Dermatology, which adds that the effect usually lasts about 3–4 months, and sometimes longer⁴.

In the controlled studies included in the Cochrane review, the average duration of effect was about 20 weeks, close to five months³. It is important to know that the effect fades gradually rather than disappearing all at once: the muscle slowly returns to its full movement, and the line gradually returns to how it was before treatment. Good evidence is still lacking on what happens to the duration of effect after a long series of repeat treatments over years³.

What are the side effects and risks?

The main significant complication is a temporary drooping eyelid, alongside milder and more common effects such as swelling and bruising. According to the Cochrane review, the risk of a drooping eyelid and similar complications, such as a mild squint or altered sensation in the eyelid, is higher than with placebo³.

The US product label carries a special warning (Boxed Warning) about the possibility that the effect may spread beyond the injection area. To be precise: at the approved cosmetic doses for facial areas, no definite cases of such serious spread have been reported⁶. A minority of patients also develop neutralizing antibodies to the substance, mainly at the higher doses used for medical rather than aesthetic indications; this is relevant mainly when a treatment that used to work suddenly stops having an effect⁷.

Is the result the same for everyone?

No. Muscle strength, skin thickness and personal expression habits all affect the result, which is why the accepted approach is individual tailoring rather than a uniform "recipe" for everyone. The international consensus on the subject stresses that the decision about the injection area and its strength is made according to a personal assessment of each patient's active muscles, not according to a fixed table¹. This is why, even between two people with a similar-looking line, the result and the experience of the treatment can differ. There are also differences in planning between women and men, detailed on the page aesthetic treatments for men.

Who should be cautious, or is less suited to the treatment?

Injections are not given when there is a known sensitivity to botulinum toxin or an infection at the injection site, and particular caution is needed with neuromuscular diseases, pregnancy and breastfeeding. This is according to the US label of one of the botulinum toxin products for aesthetic use (October 2024 update)⁶.

• Explicit contraindications: known sensitivity to any botulinum toxin product or to one of its ingredients, and infection at the planned injection site.
• Neuromuscular diseases: in people with such a disease, the risk of muscle weakness, double vision, drooping eyelid and difficulty swallowing or speaking is higher.
• Pregnancy and breastfeeding: there are not enough data on safety in pregnancy, and there are no data on passage of the substance into breast milk or on effects on the baby. In the absence of data, it is customary to postpone aesthetic treatment until after this period.
• Certain medications: aminoglycoside antibiotics and other drugs that affect neuromuscular transmission may increase the effect of the substance.
• Under 18: safety and effectiveness for aesthetic use have not been studied.

Anyone taking blood thinners or any other regular medication should mention it in the conversation with the doctor before treatment. Do not stop such a medication on your own.

What do you do after a botulinum toxin injection?

Do not rub or massage the injection area, and wait about two hours before strenuous exercise. These are the two instructions published by the American Academy of Dermatology⁴. You can return to your routine immediately after treatment, and swelling, redness or a small bruise at the needle site usually pass within days⁴.

Longer lists of "don'ts" circulate online: do not lie down for a few hours, do not drink alcohol for two days, do not bend over. We did not find a basis in controlled research for most of them, so they are not included here. Contact a doctor immediately if difficulty swallowing, speaking or breathing appears, or weakness that spreads beyond the treated area⁶.

Why is it important to have the injection from a doctor, in a clinic?

In Israel botulinum toxin is a prescription medicine, and injecting it is a medical procedure performed by a doctor. Dentists may inject only in the mouth area and within the limits defined in the Israeli Ministry of Health guidelines, not in other areas of the face⁵.

The risk of treatment outside a medical setting is real. A 2019 report by Israel's State Comptroller documented non-medical injection events in Israel held in private homes, hair salons and beauty salons, contrary to Ministry of Health instructions, as well as seizures of counterfeit products posing as hyaluronic acid and botulinum toxin⁵. In China, 161 cases of botulism poisoning were documented after illegal cosmetic injections; in about half of them the product came from an unknown source and the injection was given by an unlicensed practitioner⁸. These are reminders that the source of the product and the training of the injector matter no less than the product itself.

What is low-dose botulinum toxin, and what is intradermal injection?

These are two marketing terms worth knowing so as not to be confused, and they are not agreed medical definitions. A lower-than-usual dose, sometimes marketed under a brand-style nickname, usually describes a subtler result, but it has no uniform definition in research, and there are no controlled comparisons showing an advantage over a regular dose. Details, including what is known about the claim of "preventing" lines at a young age, are on the page low-dose botulinum toxin.

Intradermal injection of botulinum toxin (as opposed to injection into the muscle) is a use aimed at improving overall skin quality rather than relaxing a specific muscle; it too is sometimes marketed under a brand-style nickname. A systematic review of 10 small studies, 153 participants in total, found improvements in skin oiliness, pore size and fine lines, but none of the studies reached the sample size needed for strong conclusions, and most of the review authors had industry ties. The fair conclusion: preliminary and promising evidence, but not yet established⁹. This is also a use outside the registered indication in Israel². A detailed explanation is on the page intradermal botulinum toxin injection.

What is the difference between botulinum toxin and a filler?

Botulinum toxin relaxes a muscle that creates a line through movement, while a filler adds volume or smooths a fold caused by tissue loss. Expression lines on the forehead and between the brows usually respond to botulinum toxin, whereas folds such as the nasolabial fold, or loss of volume in the cheeks and lips, are usually treated with hyaluronic acid filler. The two are sometimes combined in the same area of the face when there is both muscle movement and volume loss, but they are two completely different substances in composition, mechanism of action and regulatory approval in Israel: one is a prescription medicine, the other a medical device⁵.

Can botulinum toxin be combined with other aesthetic treatments?

Yes, combining treatments in the same area of the face or in adjacent areas is common, because each treatment works through a different mechanism. Botulinum toxin treats lines created by muscle movement, so it is sometimes complemented with a filler for folds caused by volume loss, or with a collagen stimulator for gradual improvement of overall skin quality. The decision about combining, the order and the timing between treatments is made at a personal examination and depends on the overall goal.

Products used at the clinic

The three well-known botulinum toxin products are described on a separate page:

• Types of botulinum toxin and the differences between them: why the units are not interchangeable, what is known about complexing proteins, spread and duration of effect, and what is registered in Israel for each product.

What does a botulinum toxin consultation with Dr. Dana Buchbut look like?

With Dr. Dana Buchbut, a physician with 16 years of experience in aesthetic and hair medicine, botulinum toxin treatment starts with a conversation and an examination, and only then the injection. Muscle movement is assessed and your goal is clarified, and only then are the areas and dose decided. Clinical experience that includes Harvard-affiliated Brigham and Women's Hospital, together with ongoing updating on new technologies and approaches, informs every plan. The treatment is tailored individually, and at the follow-up it can be fine-tuned according to your response.

Terms on this page (glossary in Hebrew): hyaluronic acid · Radiesse (CaHA) · biostimulator · dissolvable threads · full glossary

The information on this page is general and for education only. It does not replace an examination, diagnosis or personal medical advice. A decision about treatment is made only after an examination.