1. What a filler actually is
Most dermal fillers used in the UK are gels of hyaluronic acid, a sugar molecule that occurs naturally in skin and connective tissue. The manufactured version is cross linked to make it hold its shape and resist being broken down quickly. How heavily it is cross linked determines how firm the gel is, how much lift it gives against tissue pressure and how long it lasts, which is why a gel designed for the deep cheek is not the same product as one designed for fine lines under the eye.
Other materials exist. Calcium hydroxylapatite and poly-L-lactic acid work partly by stimulating the body's own collagen response over months. Polymethylmethacrylate and various permanent gels do not break down at all. The one property that matters most to a patient is whether the material can be dissolved if something goes wrong, and only hyaluronic acid can.
2. What they do well
Fillers are good at replacing volume. Faces lose fat, bone and soft tissue support with age, and they do it unevenly: the temple hollows, the mid cheek flattens, the area beside the mouth deepens, the jawline softens. Putting structure back where structure has gone is the thing fillers do that nothing else non surgical does as directly.
They are also good at contour changes that are additive rather than subtractive: a chin projected slightly forward, a jaw angle defined, a nose bridge straightened in profile, a temple filled so that the brow no longer looks skeletal. All of those are additions.
3. What they cannot do
They cannot tighten skin. Loose skin injected with gel becomes loose skin with more volume behind it, which sometimes looks better and sometimes looks heavier. The word "lift" in filler marketing describes a visual impression created by adding support higher up the face. It is not tightening, and it is not surgery.
They cannot fix a line that is caused by muscle movement. That is botulinum toxin territory, and confusing the two is the most common reason a patient is disappointed by a technically adequate treatment.
They cannot improve skin quality. Texture, tone, pigmentation and crepiness are not volume problems. Some injectables in the adjacent skin booster category make claims in that direction, and those claims deserve their own scrutiny.
And they cannot be relied on to look the same in three months as they do on the day. Swelling is real for a week or two, and product settles and integrates for longer than that. Anyone judging the result at day two is judging the swelling.
4. Why anatomy is the whole job
The face is full of arteries, and several of them run in predictable but variable places close to the sites injectors work in. The serious complication of filler is not a lumpy result. It is vascular occlusion: gel entering or compressing an artery, cutting off the blood supply to the tissue that artery feeds. Untreated, that causes skin death. In rare cases, when the vessels involved connect towards the eye, it causes visual loss.
This risk is not evenly distributed. The nose, the area between the brows, the nasolabial fold and the under eye are higher risk zones. A non surgical rhinoplasty is a high risk procedure performed in a small space near vessels that connect to the ocular circulation, and it is routinely advertised as a lunchtime treatment.
5. How long they last
Manufacturers describe durations from around six months to two years depending on the gel and the site. In practice, filler in an area that moves constantly, such as the lips, breaks down faster than filler in a static area such as the deep cheek or the chin. Metabolism, exercise and injection depth all shift the number.
What complicates the picture is that imaging studies have repeatedly found filler still present in tissue long after patients were told it would be gone, sometimes years later, and sometimes in a different place from where it was put. That is a good reason to treat conservatively and to be sceptical of a plan that assumes a clean slate every twelve months.
Hyaluronic acid filler, one millilitre, single session
A millilitre is a volume, not a treatment. The same millilitre placed carefully into three sites by an experienced injector who spent forty minutes assessing you is a different purchase from the same millilitre pushed into one site in eight minutes.
Product cost varies by several fold across the gels on the market, and firmer, longer lasting gels cost more. The rest of the range is time, assessment, indemnity and whether the clinic can and will manage a complication rather than send you elsewhere.
An indicative editorial band, not a survey, not a quote and not a recommendation. How we build these bands.
6. The risk list, ordered by how much it should worry you
Expected and self limiting: swelling, bruising, tenderness, temporary lumpiness that settles as the gel integrates.
Common enough to plan for: asymmetry, a visible or palpable lump, a bluish tinge where superficial gel scatters light under thin skin, and product that has migrated from where it was placed.
Uncommon but serious: infection, including late onset inflammatory nodules that can appear months or years afterwards and sometimes follow an unrelated illness or vaccination; delayed hypersensitivity; and biofilm formation.
Rare and urgent: vascular occlusion. This is the one that has to be recognised within hours, not days, and the one that determines whether the person treating you needs to hold hyaluronidase, know the protocol and be reachable out of hours. Ask that question before treatment, not after.
7. The regulatory picture in Scotland
Filler is a device. Devices in the UK are regulated by the MHRA for safety and conformity marking, not by controlling who administers them. There is no requirement for a prescription and no restriction on who may buy most of them.
Whether the premises you are treated in are regulated at all depends on who is treating you. If the service is provided by a doctor, dentist, nurse, midwife or dental care professional, it generally falls within the independent clinic definition that Healthcare Improvement Scotland registers and inspects. If it is provided by someone who is not a regulated healthcare professional, it generally does not. We set that out fully in how cosmetic clinics are regulated in Scotland.
8. Before you agree to anything
Ask what gel is being used and why that one for that site. Ask how many millilitres, over how many sessions, and what the plan is if you want less rather than more. Ask whether the clinic holds hyaluronidase on the premises, who can prescribe it and what the out of hours arrangement is. Ask what happens, and what it costs, if the result needs adjusting.
Then ask yourself the harder question: is the thing you dislike actually a volume problem. A great deal of filler is sold to people whose complaint was about skin, tiredness or photographs taken at an unflattering angle. Volume was never going to fix any of those.