1. What the injection physically does
Botulinum toxin type A blocks the release of acetylcholine at the junction between a nerve ending and a muscle fibre. Without that chemical messenger the muscle cannot contract normally. Injected into a small, specific muscle in the face, it reduces how hard that muscle pulls. The nerve endings sprout new connections over the following months, the signal returns, and the muscle works as it did before.
Everything a patient wants to know follows from that one mechanism. The effect is on muscle, not skin. It is temporary because nerves regenerate. It is local because the dose is small and placed precisely. And it is entirely dependent on the muscle in question being the actual cause of the line you dislike.
2. Dynamic lines, static lines, and the difference that decides everything
A dynamic line appears when you move. Frown, and two vertical lines rise between the brows. Raise your eyebrows, and horizontal lines appear across the forehead. Relax, and they go. Those lines are made by muscle, so reducing the muscle pull reduces the line.
A static line is there when your face is still. It is a crease that has been folded into the skin so often, for so long, that the collagen and elastin underneath have remodelled around the fold. Toxin will soften the movement that keeps deepening it, and over months of consistent treatment a static line may become shallower. It will not erase one. If the line is visible in a photograph of your face at complete rest, expect improvement, not removal.
This distinction is the single most useful thing a patient can take into a consultation. A practitioner who explains it without being asked is telling you something about how they work.
3. The areas where it reliably works
The three areas treated most often are the glabella (the frown lines between the brows), the forehead and the crow's feet at the outer corner of the eye. These are the areas where the muscle is superficial, the anatomy is predictable and the relationship between muscle action and line is direct.
Beyond those, toxin is used for a widening set of purposes: softening a gummy smile, relaxing the platysmal bands of the neck, reducing the pull of the depressor muscle that turns the corners of the mouth down, slimming a heavy masseter at the jaw angle, and treating excessive underarm sweating, which is a recognised medical use rather than a cosmetic one. These are more technical, more dependent on the injector's anatomical knowledge, and less forgiving of a poor mental model of what the muscle is doing.
4. The things it cannot do, whatever the advert says
It cannot add volume. If your complaint is that your cheeks have flattened or your temples have hollowed, toxin is the wrong tool and dermal fillers are a different conversation with different risks.
It cannot lift skin that has descended. Marketing language about a "lift" from toxin refers to a small change in brow position achieved by relaxing the muscles that pull the brow down, which is a rebalancing of opposing forces, not a lift in any surgical sense. Expect millimetres, and expect them to be subtle.
It does nothing for skin quality. Texture, pore size, pigmentation, dullness, laxity and fine crepey skin are all outside its mechanism. Those belong to sun protection, topical treatment, resurfacing and time. If a treatment plan proposes toxin for a skin quality complaint, the plan has not understood the complaint.
And it cannot fix a face that is unhappy for reasons that are not on the face. A practitioner who notices that and slows down is doing the most valuable part of the job.
5. How long it lasts, and why the answer keeps changing
The usual answer is three to four months, and for most people in most areas that is about right. What changes it is dose, muscle bulk, metabolism, how expressive you are and where it was placed. Strong muscles in a physically active person tend to recover sooner. Small doses placed for a soft result wear off sooner than larger doses placed for a frozen one, which is a trade rather than a failure.
Repeated treatment over years does tend to lengthen the interval, because a muscle that has been working less is a smaller muscle. That is a real effect, and it is also the mechanism behind the most common overtreatment pattern: a forehead that has become so weak that the brow drops and the patient starts requesting more of the thing that caused it.
Botulinum toxin, one treatment area, single session
The product itself is a small part of the cost. Most of what you pay for is the prescriber's time, the assessment, the indemnity, the premises and the review appointment, and those vary enormously between a room above a salon and a registered clinic with a named doctor on call.
The low end of this band usually signals one of three things: a small dose, no prescriber consultation of any substance, or an introductory price designed to start a course. The high end usually signals a doctor or dentist injecting, a longer assessment and a follow up built in.
An indicative editorial band, not a survey, not a quote and not a recommendation. How we build these bands.
6. What can go wrong
Common and self limiting: small bruises, tenderness, a headache for a day or two, and a slight asymmetry that settles as the product takes full effect over ten to fourteen days.
Less common and more troubling: a drooping eyelid or brow when product spreads to a muscle that was not the target, a frozen or heavy feeling, an unnatural raised arch at the outer brow, and a smile that has become uneven. These resolve, because everything toxin does resolves, but they resolve on the drug's timetable rather than yours, which can mean weeks of looking like someone you did not agree to look like. That timetable is the reason a first treatment should be conservative.
Serious systemic effects from cosmetic dosing are rare. Anyone who develops difficulty swallowing, breathing or generalised muscle weakness after treatment should seek urgent medical attention and the reaction should be reported through the MHRA Yellow Card scheme, which exists precisely so that rare events are visible.
7. Who is allowed to inject it in Scotland
This is where Scotland diverges from what many patients assume. The medicine must be prescribed by an appropriate prescriber. The act of injecting it, however, is not restricted to a healthcare professional in the same way, and premises where only non healthcare professionals treat patients sit outside the registration system that Healthcare Improvement Scotland operates. We have set that out in detail in how cosmetic clinics are regulated in Scotland and in when a non medic injects.
The practical version: ask who is prescribing, whether that person will see you, and who you call at ten o'clock at night if your eyelid drops. If those three answers are vague, the price is not the problem.
8. What to ask before you agree
Ask which specific muscles are being targeted and why. Ask how many units, not how many areas. Ask what the result will look like at two weeks and at three months. Ask what happens if it is asymmetric, whether a review appointment is included and whether an adjustment costs extra. Ask who prescribed it, and whether that person has assessed you. Our full list is in the questions to ask before any injectable treatment.
A good injector will answer all of that without defensiveness, because they have thought about it already. Defensiveness at the question stage is information you are being given for free.