Does Soft Focus Always Require a Smoother Surface?

The small assumption behind a familiar formulation goal

A soft-focus formula is often asked to make pores and fine lines less visible. It is easy to translate that request into a simpler target: fill the unevenness and make the surface as smooth as possible. Yet physical smoothness and a softer visual appearance are not interchangeable measurements.

A 2025 skin-optics study makes that distinction worth examining. Some fine surface features may help redistribute light rather than merely create unwanted visible texture. This does not mean rougher skin is preferable. It raises a more useful question: are the features we want to conceal and the interfaces that help spread light necessarily the same thing?

One surface contains more than one scale of texture

Lai and colleagues collected 60 cheek-skin replica specimens, scanned their topography and separated larger furrows from finer, subvisible texture. They constructed a two-dimensional ray-tracing model and benchmarked optical predictions against two types of PMMA plate. This was not a 60-person trial of a cosmetic formulation.

Within the studied parameter range, a smaller microtexture width-to-height ratio was associated with broader simulated angular scattering. A sample previously rated visually softer showed a broader distribution but a lower peak than the comparison sample. The shape of a feature therefore matters, not simply a single average-height roughness number.

The specimen associations and model changes do not demonstrate that deliberately increasing microtexture on a person's face will improve appearance. The model is simplified, two-dimensional and single-layered; subsurface chromophores and multilayer interactions are not explicitly resolved. Its contribution is to challenge a blanket assumption that flatter must always look softer. See Methods, Figure 2; benchmark validation; Results, Figures 5-6 and Table 2.

A particle can remain in a film without scattering strongly

Would choosing a more elaborate particle structure solve the problem? Yoon and colleagues' 2020 study provides an important qualification. They investigated porous PMMA microspheres and hybrid particles carrying titanium dioxide at their surfaces, then incorporated different particles into an acrylate resin.

Printed logos remained clear beneath films containing PMMA alone. Films containing titanium dioxide or the hybrid particles appeared more opaque and blurred. The authors attributed part of this difference to refractive-index contrast: an interface between optically similar materials may scatter relatively little even though the particles remain physically present.

Surface geometry is consequently one line of explanation; the optical difference between a particle and its surroundings is another. A dry-powder image cannot settle the behaviour of the finished film. Nor did this experiment independently isolate every influence of refractive index, particle size, porosity and surface structure. See Methods 2.3-2.4 and Results 3.2, Figure 6.

More reflected light is not a complete soft-focus score

In the 2020 study, the reported diffuse reflectance at 600 nm was 10.0 +/- 0.4% for the unfilled resin film, 12.7 +/- 0.2% for porous PMMA PP3, 56.6 +/- 0.8% for titanium dioxide T2 and 62.0 +/- 1.1% for hybrid PP3@T2. These are selected values from Tables 2-3, not a ranking of cosmetic efficacy. The uncertainty notation is retained as reported without assigning an additional error definition.

The UV-cured acrylate films were 150 micrometres thick. Particle-containing preparations used 0.5 g of particles with 9.5 g of resin, measured against a black substrate with a contact probe. That 5% is an experimental loading, not a recommended cosmetic use level.

The authors also measured a soft-focus factor, but used particles mixed with nitrocellulose collodion on a black substrate for the angular-scattering test. The two matrices must not be treated as one experiment proving that greater reflectance inevitably produces better soft focus and a more natural finish.

The skin model offers a related caution: a wider angular distribution and a higher average reflectance are not the same endpoint. Background-detail visibility, peak highlights, overall brightness and colour shift need separate evaluation. Neither paper directly ranks natural-looking makeup across skin tones and lighting conditions. See the particle study's Methods 2.3-2.4 and Results 3.2-3.3; the skin study's Results, Figures 5-7.

Which explanation survives the comparison?

The simplest explanation is that geometry determines soft focus. The skin model supports a contribution from geometry, but the hybrid-particle study also changes optical contrast, particle size, pores and interface arrangement. Its improvement cannot be assigned to roughness alone.

The opposite explanation, that a high refractive index explains everything, is also incomplete. With a prescribed skin refractive index, the first model still produces different angular distributions when microgeometry changes. That does not establish that the same relationship transfers unchanged to a particle-containing cosmetic film.

The studies are complementary, not contradictory arms of a matched trial. One examines a modelled skin surface, the other particles inside model films. Neither directly bridges these settings to a complete formulation dried on skin.

Muzi's provisional hypothesis is therefore specific: in some formulations, reducing the visibility of larger furrows and retaining useful microscale scattering interfaces may need to be designed together. Maximising smoothness or a powder's isolated scattering score might miss that combination. This is an editorial hypothesis, not an established formulation rule.

Four experiments that could separate the explanations

First isolate geometry as far as practical. Prepare the same formulation under flat, broad-feature and fine-feature film-forming conditions while matching dry mass per area and film thickness. Record topography, dispersion and porosity, then measure angular width, the specular peak and reflectance. If the texture-making process also changes aggregation or pores, those remain confounders. Reproducible angular changes would support a geometric contribution; only increased reflected intensity would require checking thickness or opacity instead.

Then compare two candidate powders in two compatible carriers, giving four combinations. Match particle volume fraction, dry-film thickness, dispersion and final topography as closely as possible, and measure the dry carrier's optical properties. A wet oil's refractive index does not fully specify a dried film. Predeclare the primary endpoint and a difference exceeding measurement repeatability. A reproducible interaction could support carrier-dependent ranking; stable rankings and differences would weaken that hypothesis for these systems.

Connect optics to a defined visual endpoint. Use textured model substrates and contrast targets across background colours, lighting directions and viewing angles. Lock exposure and white balance; analyse texture contrast, mean brightness, colour shift and highlights separately, followed by blinded image ratings. A higher instrument score without improved ratings, or with conspicuous whitening, would weaken its relevance to natural appearance. Model-substrate results are not human efficacy evidence.

Finally test whether the interface persists. Repeat independent preparations and remeasure morphology and angular distribution at predefined drying times and before and after simulated sebum contact and standardised rubbing. Track film loss so removal is not mistaken for an intrinsic interface change. If the initial advantage disappears or batch variation exceeds the formulation difference, process and film stability should be resolved before claiming a useful technical advantage. These four experiments are proposed by Muzi and have not been performed.

A conditional prediction, and reasons to abandon it

Muzi's prediction is not that a new class of powder will displace existing materials. It is that evaluation may move one step downstream: from the ingredient alone to the film it forms in the intended carrier. Suppliers would specify the test matrix, film-forming conditions, observation geometry and optical endpoint alongside particle data. Formulators would use a crossed comparison instead of treating one benchmark ranking as universal.

For a customer, the question becomes more concrete: which visible texture should become less apparent, under which lighting, and with what acceptable changes in brightness and colour? Adoption would still depend on repeatability, cost and whether extra measurements reduce formulation trial and error. Neither study proves this market prediction.

We would lower the priority of microtexture design if its apparent effects vanished after controlling thickness, dispersion and optical parameters. We would stop treating an optical change as a meaningful advantage if it failed to track texture visibility or blinded ratings. Stable powder rankings across carriers and use conditions, with little benefit from extra testing, would favour a simpler evaluation method.

Does soft focus always require a smoother surface? The defensible answer is that flatter cannot simply stand in for visually softer. What needs designing and testing is the final interface, how it redistributes light, and whether that change improves the particular visual problem that matters.

Source context and limits

The 2025 Scientific Reports study, by Lai and colleagues, involved researchers associated with A*STAR and P&G; the authors declared no competing interests. Its evidence combines specimen associations with simplified optical modelling, not a finished-product intervention.

The 2020 Polymers study, by Yoon and colleagues, was supported by Cosmax and the Korean National Research Foundation; the authors declared no conflict of interest. It is a laboratory particle-and-film study, not a human cosmetic trial. Both full texts are available under CC BY 4.0. This article reorganises their evidence and distinguishes Muzi's proposed interpretation from their findings. It makes no claim of skin repair, anti-ageing or other biological efficacy.