24 SUN CARE Due to their organization, water-in-
liquid crystal emulsions offer multiple benefits in beauty formulations, producing a stable emulsion against a coalescence of water droplets and sensoriality, where the liquid-crystalline structure impacts product consistency and contributes to the fluidity and dynamism of this meshwork when applied to the skin. The large amount of water trapped in the emulsion is available immediately when the cream is applied to the skin. For this reason, the emulsions have a shiny appearance and a light, fresh-touch texture similar to oil-in-water emulsions.
The sensory benefit of water-in-oil
emulsions with a high external phase content has been demonstrated by the evaluation of two water-in-oil emulsions with UV filters content. The use of GE as an emulsifier for sunscreen formulations allows the formation of water-in-liquid crystal emulsions with 8% to 23% more water than standard non-ionic emulsifiers such as Sorbitan Oleate or Glyceryl Oleate. Table 1 represents the composition of W/O
test emulsions, one W/O with high water content based on Isostearyl Glyceryl Ether as emulsifier and Lauryl Lactate as solubilizer (ref. GE) and two standard W/O emulsions based on Sorbitan Oleate or Glyceryl Oleate as emulsifier and C12-15 Alkyl Benzoate as solubilizer (ref. SO & GO).
The sensory evaluation of the three
sunscreen formulations was carried out with an expert panel (Figure 5). Panellists were asked to rate attribute intensity using structured five-point scales, scoring from 1 (low) to 5 (high) during and after emulsion application. The test coordinator placed 14 ml (2 mg/ recommended amount of sunscreen to be
cm2
applied; ISO 24444) on the inner side of the forearm of the panellists. The latter evaluated the following attributes: ease of spreading, absorption and oiliness. Ease of spreading was evaluated during
application; absorption was evaluated immediately after application; and oiliness was evaluated immediately after application and again after five minutes.3 The W/O emulsion stabilized with GE was
perceived as a standard Sorbitan Oleate-based W/O emulsion in most of the sensory attributes tested, with the exception that it produced a less greasy skin feel than conventional W/O emulsions. These results were consistent with the
results obtained by sebum level quantification. 5 3 1 Oiliness 5 3 1 Absorption GO ■ SO ■ GE ■
Sensory assessment After
application 5 3 1 Oiliness
5 3 1 Spreadability
Application
Figure 5: Sensory assessment profile during application and after application of the sunscreen formulations to the forearm of the panellists
Adhesive patches (Sebutape) were applied to the inner side of the forearm of the panellists where 14 ml of sunscreen formulation was applied. The Sebutape was removed after 15
minutes and the sebum level was read using the criteria described in Figure 6. The water- in-oil emulsions with a high external phase content based on GE showed lower sebaceous secretion levels than standard W/O emulsions.
Conclusion The use of Exceparl LM-LC (Lauryl Lactate) and Penetol GE-IS (Isostearyl Glyceryl Ether) in the re-designed sunscreen formulations have overcome some of the formulation challenges with a view to developing eco-sustainable sunscreens. We recommend the use of Exceparl LM-
LC as a solubilizer for sunscreens because it shows high solubilization capacity and good dispersion of inorganic UV filters with low viscosity.
Sebutape Readings 1 2 PERSONAL CARE June 2024 3 4 Increasing sebum level Figure 6: Sebaceous secretion levels for each sunscreen formulation, assessed with a scoring scale
www.personalcaremagazine.com 5
5 4 3 2 1
GE GO SO
Likewise, we recommend the use of Penetol GE-IS as an emulsifier to create water-in-liquid emulsions with a high content of external phase, providing benefits in the stability of emulsions where the organization of water in the liquid crystal emulsion prevents the coalescence process and affords a light and non-greasy touch on the skin. In conclusion, a sunscreen formulation is
obtained that can guarantee that it will be appreciated, applied and reapplied, thereby improving its effectiveness.
PC
References 1. Spruce B, Souza A, Copsey E. Croda Europe. Working with TiO2
UV filters in powder form. Personal Care Global. May 2022
2. Suzuki Y, Tsutsumi H. Emulsifying Characteristics of α-monoalkyl glyceryl ether. Ukagaku. 1987; 36, 588
3. Parente ME, Gámbaro A, Ares G. Sensory Characterization of Emollients. Journal of Sensory Studies. 2008; 23:149-161
Sebutape readings
Sebum Level
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