The topic is short and compact
The claimed sun protection factor must be tested on the finished product and cannot be derived from the filter concentration.
For broad-spectrum protection, the EU requires UVA protection of at least one-third of the claimed SPF and a critical wavelength of 370 nm.
The test according to ISO 24444 is carried out with 2.0 mg/cm2, which is significantly more than consumers apply in everyday life.
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The expectation for daily sun protection is contradictory: high protection combined with a texture that feels like a light day cream. However, high protection requires a high amount of filters, and filters are either solids that must be dispersed or oil-soluble substances that require a large oil phase.
Both place a strain on the emulsion. Oil phase proportions beyond about one third significantly increase the tendency to creaming and phase separation. At the same time, the product should not be greasy, leave no white cast, and be suitable for wearing under makeup. This combination is the real development challenge.
High protection requires high filter amounts and thus a strained emulsion.
Mineral filters tend to leave a white cast and agglomerate.
Organic filters require a large, carefully balanced oil phase.
Why daily SPF care is technically difficult
The expectation for daily sun protection is contradictory: high protection combined with a texture that feels like a light day cream. However, high protection requires a high amount of filters, and filters are either solids that must be dispersed or oil-soluble substances that require a large oil phase.
Both place a strain on the emulsion. Oil phase proportions beyond about one third significantly increase the tendency to creaming and phase separation. At the same time, the product should not be greasy, leave no white cast, and be suitable for wearing under makeup. This combination is the real development challenge.
High protection requires high filter amounts and thus a strained emulsion.
Mineral filters tend to leave a white cast and agglomerate.
Organic filters require a large, carefully balanced oil phase.
Mineral, organic or combined
Mineral filters such as zinc oxide and titanium dioxide act primarily physically and are suitable for positioning on sensitive skin. Their disadvantage is the whitening effect, which is clearly visible on darker skin types, as well as the tendency to agglomerate, which deteriorates both the texture and the actual protection.
Organic filters absorb UV radiation and allow significantly lighter, transparent textures. However, they require careful selection from the approved list and may be less well tolerated on damaged skin. In practice, combined systems are the most common approach because they balance protective performance and sensory profile.
Zinc oxide: broad spectrum, photostable, suitable for sensitive positioning.
Titanium dioxide: predominantly UVB, requires very good dispersion to prevent whitening.
Organic filters: light textures, but narrower regulatory selection.
Dispersion determines protection and texture
With mineral systems, dispersion is the single most important factor. Agglomerated particles scatter light differently than individually distributed ones, which reduces the measured protection and at the same time creates a gritty skin feel. Both problems have the same cause.
Surface-treated pigments and pre-dispersed concentrates solve this much more reliably than adding powder directly to the batch. The relationship between dispersion and result is the same as in color cosmetics, as described in Shade Development for Makeup.
Pre-dispersed concentrates instead of adding powder to the batch.
Surface-treated particles for better wetting.
Document dispersion time as a binding process parameter.
What the EU demands
Sunscreen products are cosmetic products in the EU and are subject to Regulation (EC) 1223/2009. Only filters from the approved list in Annex VI may be used, in each case within the maximum concentrations specified there.
Additional requirements apply to claims: minimum protection, UVA protection of at least one third of the claimed sun protection factor, and a critical wavelength of at least 370 nm for claiming broad-spectrum protection. The framework for this is described in EU Cosmetics Regulation in Practice.
Only approved filters from Annex VI, within the maximum limits.
UVA protection at least one third of the claimed SPF.
Critical wavelength at least 370 nm for broad-spectrum protection.
The sun protection factor is tested, not calculated
The most important point for planning: the sun protection factor cannot be derived from the filter concentration. It depends on the entire formulation matrix, on the film formation on the skin, the droplet size of the emulsion, and the distribution of the filters. Two formulations with an identical amount of filters can achieve significantly different values.
Proof is provided on the finished product, usually in vivo according to ISO 24444 with a defined application quantity of 2.0 mg/cm2. This amount is significantly higher than what consumers apply in everyday life, which is why a pleasant texture is not only a selling point, but also increases the likelihood that a sufficient amount is applied.
In vitro pre-screening for estimation before expensive in vivo testing is conducted.
In vivo testing according to ISO 24444 on the finished product in its final packaging.
Plan for time and cost buffers for potential readjustment.
Packaging and scale-up
Packaging in this category is functional. Organic filters are sometimes sensitive to oxidation and light, which is why low-air systems and opaque materials maintain protection throughout the shelf life. For mineral suspensions, the opening geometry also determines whether the product can be dispensed evenly.
During scale-up, energy input is critical. The dispersion achieved in the laboratory must be reproducible on a production scale, otherwise the tested protection in series production will be lower than in the prototype. Likewise, temperature control must be tightly managed so that organic filters do not recrystallize. The methodology for this is found in Scaling Up Cosmetics Production.
Low-air and opaque systems for sensitive filters.
Check material compatibility, as filters can be absorbed by the packaging material.
Establish dispersing and temperature parameters in the pilot batch.
Double-check protective efficacy on production-run samples, not just on laboratory samples.
More useful links
FAQ
Can the sun protection factor be calculated from the amount of filter?
No. The sun protection factor depends on the entire formulation matrix, including film formation, droplet size and filter distribution. Two formulations with identical filter concentrations can achieve significantly different values. Proof is provided on the finished product, usually in vivo according to ISO 24444.
What UVA protection does the EU require?
The UVA protection factor must be at least one-third of the declared sun protection factor. To claim broad-spectrum protection, a critical wavelength of at least 370 nm is also required. Both are verified on the finished product.
Why is it tested with 2.0 mg/cm2 when nobody applies that much?
Because the test must be reproducible. ISO 24444 defines this application amount so that results are comparable between laboratories and products. In everyday life, much less is applied, which is why a pleasant texture increases the likelihood that a sufficient amount of product is used.
Why do mineral filters leave a white cast and what can be done about it?
Whitening occurs due to light scattering on the particles and intensifies when they agglomerate. Surface-treated pigments, pre-dispersed concentrates, and sufficient dispersion time significantly reduce this effect. The same measure simultaneously improves the measured protection.
Which packaging is suitable for SPF products?
Airless systems, such as airless dispensers, and opaque materials, because many organic filters are sensitive to oxidation and light. For mineral suspensions, the opening geometry is also relevant to ensure the product can be dispensed evenly. Material compatibility must be tested.
What is most critical during scale-up?
The energy input during dispersion and the temperature control. If the dispersion on a production scale is incomplete, the tested protection will be lower than in the laboratory sample. Too high or too long heat exposure can cause organic filters to recrystallize. Both parameters must be established in the pilot batch.
