Before anything else, work out which lines you mean. People use "smile lines" for both, and the treatments are completely different.
These are the small lines that fan out from the outer corner of each eye when you smile. Doctors call them lateral canthal lines.
They are made by the ring of muscle around the eye squeezing when you smile. Relax that muscle and the lines soften. This is exactly what botulinum toxin is for, and crow's feet are one of the most commonly treated areas on the face.
Published consensus for Dysport describes about three injection points per side, at roughly 5 to 10 Speywood units per point.
One thing to know: in the United States, Dysport is approved only for the frown lines between the brows. Treating crow's feet with it is off-label. That is legal, extremely common, and not a warning sign — but it does mean the FDA did not review a dose for that area. Botox Cosmetic and Xeomin do carry approvals for crow's feet, since 2013 and 2024.
These are the two lines running from the sides of your nose to the corners of your mouth. They deepen with age and are often the ones people mean by "smile lines" or "laugh lines."
Botulinum toxin is not the treatment for these, and the reason is anatomy. Nasolabial folds are sorted into three types by what is mainly driving them: loss of volume in the cheek, loosening of the skin and tissue, or where the muscle attaches under the skin. Toxin can only act on the third of those. In most people the fold is being driven by one of the first two, and no amount of muscle relaxation touches either.
Worse, weakening the muscles in that area causes a real problem. Those muscles lift your upper lip. Relax them and your smile changes — often visibly and unevenly. This is why the major consensus guidelines for lower-face treatment leave nasolabial folds off the list entirely.
The usual treatment for nasolabial folds is dermal filler, which replaces the volume that is missing. That is an FDA-approved use for filler products.
Toxin has a few genuine roles in the lower face, all off-label and all at small doses:
Those unit figures are not Dysport numbers. They come from consensus work on incobotulinumtoxinA, which is measured on roughly the same scale as Botox — not on Dysport's scale. There is no published Dysport dose for either area, and units do not convert between brands. If your injector is using Dysport around your mouth, ask for their number directly rather than checking it against these.
These are precise, low-dose treatments in a region where a small error shows up every time you talk. Over-treating the upper lip can leave it genuinely weak — enough to affect a straw, a whistle, or the way you sound. They should be done by someone who does them often.
Do not say "smile lines." Point instead, or say:
Your injector will tell you immediately which treatment fits, and they are different appointments with different products and different costs.
Go to an emergency department or call 911. These are rare, but they are the symptoms named in the FDA boxed warning that every botulinum toxin product carries, deaths have been reported, and they can begin hours or even weeks after treatment.