Speciality Chemicals Magazine MAR / APR 2026 | Seite 46

factor in this. A value of above 500 Dalton is commonly used as a practical threshold: molecules below this value are more likely to permeate the skin, while those above it are generally unlikely to penetrate and reach viable skin layers. 9

The MW of bemotrizinol is 628 g / mol, a value that strongly predicts low or negligible skin permeation. This therefore supports its suitability for use in a wide range of sunscreen applications.

Developed and first approved in Europe in 2000, bemotrizinol will become available for global use after pending FDA approval in the US, which is currently underway. In Europe in 2025, it was included in over 80 % of newly launched organic UV filter-based sunscreens. 10 Once regulatory approval is granted in the US, it will broaden consumer access to sunscreens with improved broadspectrum performance.

Regulatory approval does not automatically grant unrestricted use of a UV filter. Patents and patent applications may limit how a substance can be used. BASF owns multiple patents and patent applications

Figure 3- SPF 50 broad-spectrum sunscreen with bemotrizinol

Note: SPF in vivo 53, UVA1 / UV >= 0.70 related to the preparation and use of bemotrizinol.

A one-size-fits-all sunscreen is a myth; individuals have different needs and expectations regarding skin sensitivity, preferred application formats and sensorial preferences, or the purpose and area of intended use. Being oil-soluble, Tinosorb S can be used flexibly across all formulation types, from emulsions and sticks to non-aerosol sprays, to meet a wide range of individual needs. Figure 3 gives an example of a sunscreen composition with SPF 50.

Solubilisation considerations

A study showed that recrystallisation of a UVA UV filter reduced UVA protection by about 20 % in a representative emulsion, which is sufficient to jeopardise broadspectrum claims, depending on the SPF. 11 Recrystallisation of a UVB UVfilter would similarly lower SPF.

Bemotrizinol, like other existing lipophilic organic UV filters, is a crystalline solid and must be solubilised in the formulation ' s oil phase. It was designed with ethylhexyloxy substituents( Figure

Phase Ingredient INCI % by weight A Eumulgin BA 25 Beheneth 25 2.00 A Cutina Shine Dioctyl Pentaerythrityl Distearyl Citrate 3.00 A Cetiol B Dibutyl Adipate 10.00 A Cetiol ABV C12-15 Alkyl Benzoate 10.00 A Cetiol CC Dicaprylyl Carbonate 2.00 A Lanette 22 Behenyl Alcohol 2.00 A Preservative Preservative qs A Uvinul N 539 T Octocrylene 10.00 A Neo Heliopan OS Ethylhexyl Salicylate 5.00 A Tinosorb S Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine 6.00 A Eusolex 9020 Butyl Methoxydibenzoylmethane 3.00 B Water, demin. Aqua 37.80 B Verdessence Xanthan Xanthan Gum 0.20

B Cosmedia HP Starch Hydroxypropyl Starch Phosphate 1.00 B Tinomax CC Calcium Carbonate, Hydroxyapatite 3.00 C Verdessence RiceTouch Oryza Sativa Rice Starch 2.00

3.00

1) to enable its solubilisation in common cosmetic oils, such as benzoates, adipates, and triglycerides. Its solubility is low(< 1 %) in apolar oils like silicones, vegetable oils and hydrocarbons, highlighting the importance of appropriate emollient selection.

If the oil-phase composition( or storage / temperature cycles) drives a crystalline solid UV-filter above its equilibrium solubility, recrystallisation can occur over time. Once crystals form and multiply in the formulation, the effective UV absorbing area in the applied sunscreen film decreases, lowering the UV protection delivered

C 12-15 alkyl benzoate( Cetiol ** ABV) and dibutyl adipate( Cetiol B) repeatedly emerge as strong( and widely used) solubilisers for many crystalline UV filters, while dicaprylyl carbonate( Cetiol CC) is often used in sunscreen products to add sensorial elegance. Binary( or even more complex) oil mixtures are commonly used in sunscreens; each crystalline UV filter may preferentially dissolve in a different emollient.

To help select appropriate emollients, BASF developed the Sunscreen Simulator, which has been on the market since 2000. This digital tool predicts the performance of a chosen filter combination and provides solubility estimates for crystalline filters in a selected emollient or emollient blend. 12

Solubility measurements

The available solubility data are typically measured for each individual UV-filter in single emollients, whish is the most favourable condition for the risk of recrystallisation. The values provided by BASF tend, therefore, to be very conservative, especially for the standard emulsion sunscreens.

In practice, achieving roughly 80 % of theoretical solubility value is generally sufficient to keep bemotrizinol( but also the other crystalline solid UV filters like ethylhexyl triazine( EHT, Uvinul ** T150) and DHHB( Uvinul A Plus) dissolved in oil-in-water( O / W) emulsions. Attention must be paid to

46 SPECIALITY CHEMICALS MAGAZINE ESTABLISHED 1981