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👨🏻‍⚕️Assistant Professor
🧑🏻‍🔬Scientist at Erasmus MC
🥇Over 17.5 years of experience

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$We need to stop calling it the Tyndall effect. The blue-grey tinge after superficial HA filler gets the same reflex label every time - 'Tyndall, like the blue sky'. I have said it in lectures myself - because it's what we are all told. It is wrong, and it is slowly driving me insane... A visible blue scatter needs three things at once: particles far smaller than the wavelength of light, a refractive-index difference from the surrounding tissue, and the 1/lambda-to-the-fourth dependence that favours blue. HA filler fails on the first two. The gel particles you inject are 300-700 microns - about a thousand times the wavelength - which puts them in the regime that scatters neutral white, not blue. And the gel is around 98% water, near-index-matched to the tissue around it, so there is almost no contrast to scatter from in the first place. There is a bench test showing no scatter through HA gel; skin optics would hide any subdermal blue anyway; and - the bit that blows my brain - the same molecule is used elsewhere in tissue optics to reduce scattering, not create it. The honest bit: the imprecise size-and-wavelength language runs on both sides of this debate, including in the paper whose conclusion I agree with. That is rather the point - the taxonomy has been unreliable across the field. If it is not scattering, the best-fit explanation is the same reason your veins are blue - skin reflectance, blood absorption, observer perception - and even that is speculative. But it fits: even, often delayed, not dose-dependent. Retire the label. Call it blue-grey dyschromia. Full argument in a paper I am working on. DOI: I train for filler manufacturers - but this concerns HA as a class, not any one product, and the argument stands on the physics. Save this for the next time 'Tyndall' gets said in a training room. And tell me where the argument is wrong - I would rather be corrected than repeat a tidy myth.$

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