Toxin diffusion: what it is and why it matters
Quick facts
- Definition
- Spread of the toxin from the injection point into neighboring tissue.
- Depends on
- Volume, dilution, dose, site, technique, and patient characteristics.
- Desired effect
- Reaching the target muscle evenly.
- Undesired effect
- Reaching neighboring muscles, causing ptosis, asymmetry, or unintended weakness.
Toxin diffusion is the spread of the product, from the point where it was injected, into neighboring tissue. All botulinum toxin spreads a little: that is what allows the product to reach the target muscle. The problem appears when the amount reaching a neighboring muscle is enough to weaken it unintentionally.
What does it depend on?
Several factors act together, and none of them guarantees the outcome on its own:
| Factor | Role |
|---|---|
| Total dose | The more product, the greater the potential reach |
| Volume and dilution | Change how the liquid spreads through the tissue |
| Site | Small, neighboring muscles require more care |
| Patient characteristics | Anatomy, muscle strength, tissue mass |
| Post-procedure | The professional's instructions |
Comparisons between products, including the debate over the protein complex, do not allow one to claim that one spreads less than another. See also the toxin unit, which is not equivalent between products.
Which undesired effects resemble diffusion?
- Eyelid ptosis: a drooping upper eyelid, when the levator muscle is reached, usually from injection in the glabella and forehead.
- Lip ptosis: drooping of the lip after perioral injection.
- Asymmetric smile: when smile muscles are reached.
These conditions are generally temporary, but they last weeks, since the toxin's effect takes days to appear (latency) and months to wear off. That is why the patient should be warned beforehand.
In Harmy
At the Glabella point, Harmy projects the smoothing of the area in symbolic units, not in real product units. The projection is illustrative and does not predict diffusion or undesired effects.
Frequently asked questions
What is botulinum toxin diffusion?
It is the spread of the product from the injected point. Some diffusion is expected and necessary, but excess can reach neighboring muscles.
Does diffusion cause a drooping eyelid?
Eyelid ptosis is a described complication when the product reaches the muscle that lifts the eyelid. It is temporary, but bothersome, and management is up to the professional.