Speciality Chemicals Magazine MAR / APR 2026 | Page 47

COSMETICS & PERSONAL CARE

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Figure 4- Recrystallisation speed of bemotrizinol( BEMT) & avobenzone( BMDBM) in different formulation chassis at 4 ° C storage

the continuous lipophilic phases, such as water-in-oil( W / O) and lipophilic systems.

Vehicle & emulsifier influence

A study including 24 formulations covering different emulsifier systems( O / W, polymeric, W / O and neat oil systems) monitored the recrystallisation of four crystalline UV filters— bemotrizinol, avobenzone, EHT and DHHB— under high relative oversaturation for 20 weeks at two storage temperatures( 4 ° C and 23 ° C).

The results can be summarised in three key findings. First, vehicle continuity matters, Recrystallisation was much faster in neat oils and W / O emulsions with a continuous lipophilic phase, where nucleation propagates rapidly through a single, connected oil network.

Second, emulsifiers play a role. Certain polymeric systems( e. g., Acrylates / Beheneth 25 Methacrylate Copolymer( Tinovis ** GTC)) and anionic systems( e. g., Sodium Stearoyl Glutamate( Eumulgin ** SG)) delayed recrystallisation relative to other O / W systems. This is consistent with literature explaining that surface-active species can promote or inhibit nucleation depending on interfacial ordering and interfacial tension effects.

Third, the UV filter used matters. Under matched oversaturation, smaller / more rigid molecules( e. g., avobenzone) recrystallised faster than larger, highly flexible molecules such as bemotrizinol. Figure 4 presents the results for the two filters: bemotrizinol and avobenzone. 11

The key takeaways for the formulation playbook from this are: 1. Start with the right selection of UV filters- make Tinosorb S the core of your UV-filter system: broadspectrum protection, photostable foundation for lasting performance, photostabiliser of labile UV filters, compatible with all formulation types of spectrum protection

2. Continue with the right selection of the emollient blend for preventing recrystallisation and loss of protection

3. Leverage on formulations: continuous aqueous phase formulations tend to limit recrystallisation over time

Conclusion

The development of Tinosorb S exemplifies how research structure‐enabled photostability, high and broad-spectrum absorption, and how a single molecule can play the dual roles of primary UV-filter and stabiliser.

The industry’ s focus is unchanged: reliable, elegant broad-spectrum protection sunscreens that consumers like to use every day. User compliance drives final effectiveness of the sunscreen product. The most efficient sunscreen pairs good chemistry with good physics: photostable chromophores like bemotrizinol, placed into a vehicle engineered to keep the contained UV filters dissolved, and with memorable sensorial experience. ●

*- The authors would like to thank Diane Tom of BASF Corporation in the US

**- Tinsosorb, Uvinul Tinovis, Cetiol and Eumulginis are all registered trademarks of the BASF Group

MAR / APR 2026 SPECCHEMONLINE. COM

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