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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.
The demand for daily sun protection is contradictory: high protection combined with a texture that feels like a light day care product. However, high protection means a large amount of filters, and filters are either solids that need to 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, should not leave a white cast, and should be wearable under makeup. This combination is the real development challenge.
High protection requires high amounts of filters and thus a heavily loaded 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 demand for daily sun protection is contradictory: high protection combined with a texture that feels like a light day care product. However, high protection means a large amount of filters, and filters are either solids that need to 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, should not leave a white cast, and should be wearable under makeup. This combination is the real development challenge.
High protection requires high amounts of filters and thus a heavily loaded 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 for significantly lighter, transparent textures. However, they require careful selection within the approved list and may be less well tolerated on pre-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
For mineral systems, dispersion is the most important single 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 to the batch. The connection between dispersion and result is the same as in color cosmetics, described in Shade development for make-up.
Pre-dispersed concentrates instead of powder addition in the batch.
Surface-treated particles for better wetting.
Document dispersion time as a binding process parameter.
What the EU requires
Sunscreens 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: a minimum level of 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 of 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 filter can achieve significantly different values.
Proof is provided on the finished product, usually in vivo according to ISO 24444 with a defined application amount 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.
Allow for time and cost buffers for potential readjustments.
Packaging and scale-up
Packaging is functional in this category. 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, the 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 sample. Likewise, temperature control must be strictly managed so that organic filters do not recrystallize. The methodology for this is described in Scale up cosmetics production.
Low-air and opaque systems for sensitive filters.
Check material compatibility, as filters can be absorbed by the packaging material.
Define dispersion and temperature parameters in the pilot batch.
Double-check the protective effect on production samples, not just on laboratory samples.
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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. Verification is carried out 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 additionally required. Both are verified on the finished product.
Why is it tested with 2.0 mg/cm2 if no one 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, significantly less is applied, which is why a pleasant texture increases the likelihood that sufficient product will be used.
Why do mineral filters leave a white cast and what helps against 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 also improves the measured protection.
Which packaging is suitable for SPF products?
Low-air 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 dispersing and the temperature control. If the dispersion is incomplete on a production scale, the tested protection will be lower than in the laboratory sample. Excessive or prolonged heat exposure can cause organic filters to recrystallize. Both parameters must be specified in the pilot batch.
