30 SKIN PROTECTION
emollients, with no particle aggregation. These results provided proof of principle of
the applicability of Triethyl Citrate in achieving uniform dispersions of commercially available test material.
Sensory profiling of formulation with inorganic filters Particle dispersion is also reflected in distributability on the skin, which is an important requirement for effective protection from sun. Furthermore, emollients influence attributes related to pick up of the product, rub out and after feel on the skin, and thus consumer acceptance. To evaluate the applicability of Triethyl Citrate, a full formulation comprising only inorganic UV filters with a calculated SPF of 30 and a UVA-PF > 10 was prepared as shown in Table 5. The sensory attributes of this formulation were compared with those of two commercially available, certified natural benchmark formulations with SPF 30 and UVA protection claims. This was done by presenting the anonymised formulations to a trained sensory panel consisting of 10 panellists. The samples were ranked on a scale from 0 (attribute not pronounced) to 10 (attribute strongly pronounced). In the sensory profiling, the sunscreen
formulation with inorganic UV filters and Triethyl Citrate showed beneficial characteristics compared to benchmarks from the market. Specifically, consistency was lighter and gliding effect and distributability were more pronounced while at the same time the skin feel conferred was less greasy/oily. This resulted in faster absorption and less film residues after product application. Triethyl Citrate is therefore a promising ingredient for formulations of certified-natural sunscreen products.
Conclusion The emollients Triethyl Citrate and Tributyl Citrate showcase remarkable advantages for sunscreen formulations. The excellent solvent power of Tributyl Citrate enables cost-efficient, high-SPF formulation with extraordinary flexibility regarding co-emollients, especially when relying on EHT as an organic UV filter. Triethyl Citrate is a COSMOS-approved alternative emollient distinguished by a pleasant sensory profile in both formulations based on organic UV filters and those with inorganic UV filters. In addition, it can
ZnO (ZinClear® XP) ZnO (Z-Cote®) TiO2 (Eusolex® T-S)
Figure 4: Dispersibility of inorganic UV filters in different emollients. Scale bars denote 100 µm.
potentially boost UVA-PF and thus crucially contribute to product labelling with a UVA claim. Both citrate esters represent outstanding value in the formulator’s palette of emollients for use in sunscreens, optimising performance, costs and consumer experience.
References 1. Berardesca E, Zuberbier T, Sanchez Viera M, Marinovich M. Review of the safety of octocrylene used as an ultraviolet filter in cosmetics. Eur Acad Dermatol Venereol. 2019;33(Suppl. 7):25–33.
2. Oral D, Yirun A, Erkekoglu P. Safety Concerns of Organic Ultraviolet Filters: Special Focus on Endocrine-Disrupting Properties. J Environ Pathol Toxicol Oncol. 2020;39(3).
3. Herzog B, Giesinger J, Schnyder M. Solubility of UV Absorbers for Sunscreens is Essential for the Creation of Light Feel Formulations. SOFW Journal. 2013;139(7):7–14.
4. Sohn M, Krus S, Schnyder M, Acker S, Petersen M, Pawlowski S. et al. How to Overcome the New Challenges in Sun Care. SOFW Journal. 2020;146(7+8/20):2–10.
5. Beyere L, Yarasi S, Loppnow GR. Solvent effects on sunscreen active ingredients using Raman spectroscopy. J Raman Spectrosc. 2003;34(10):743–50.
TABLE 5: COMPOSITION OF EXAMPLE SUNSCREEN FORMULATION WITH INORGANIC FILTERS AND TRIETHYL CITRATE.
Phase A
INCI/Name Aqua Glycerine
Sodium Gluconate Xanthan Gum
B C
D E
Zinc Oxide (Z-Cote®)
Cetyl Alcohol, Glyceryl Stearate, PEG-75 Stearate, Ceteth-20, Steareth -20 (Emulium® Delta MB)
Triethyl Citrate (CITROFOL® AI) Titanium Dioxide (Eusolex® T-S) Preservative
PERSONAL CARE June 2021
Amount [%] q.s. to 100 3.0 0.2 0.4 13.1
4.0
20.0 9.0 q.s.
Film residues Secondary whitening
Absorption Sticky after feel
Gliding effect after feel
Whitening Greasy/oily
6. Sohn M, Amorós-Galicia L, Krus S, Martin K, Herzog B. Effect of emollients on UV filter absorbance and sunscreen efficiency. J Photochem Photobiol B Biol. 2020;205(2020):111818.
PC
7. Huber P. Anwendungsgebiete der Sensorik (V); Körperpflege und Kosmetika (chapter 2.3): kosmetische Produkte. In: Busch-Stockfisch, M. (ed.). Praxishandbuch Sensorik: in der Produktentwicklung und Qualitätssicherung. Behr, Hamburg (2015), 1–28.
8. Huber P. “Sense and sensibility” in der Kosmetik: die vielen Unbekannten sensorischer Testungen. In: Fischer, R. (ed.). Kosmetikjahrbuch 2008: Sensorik − Wirkung mit Gefühl. Verlag für chemische Industrie, Thannhausen (2008).
9. US Food and Drug Administration. Sunscreen drug products for over-the-counter human use: proposed rule. Federal Register 2019 p. 6204– 75. Available from: https://www.federalregister. gov/documents/2019/02/26/2019-03019/ sunscreen-drug- products-for-over-the- counter-human-use
10. Szabados Z, Aikens P. Zinc oxide − an effective and versatile broad spectrum UV absorber for sunscreens and daily wear products. Euro Cosmetics. 2014;5:25–29
11. Gripp A, Paraszczuk N, Brito J. Best practices for formulating sunscreen with ZnO. Happi. 2020.
Stickiness 0
9 8 7 6 5 4 3 2 1
Stringiness
Gliding effect at rub-out
Consistency at pick-up
Distributability
Consistency at rub-out
Benchmark 1 ■ Benchmark 2 ■
Formula with Triethyl Citrate ■
Figure 5: Sensory profiling of sunscreen with Triethyl Citrate compared to commercially available natural-certified benchmarks. Values are means of n = 10.
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Caprylic/Capric Triglyceride
Coco Caprylate/Caprate
Triethyl Citrate
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