SUN CARE 67
Assessing the Radical Potential For manufacturers to meet this important consumer concern, BASF researchers have teamed up with experts from the Gematria Test Lab and found a way of efficiently testing formulations. They used a method based on Electron Spin Resonance Spectroscopy (ESR), developed and protected by Gematria Test Lab, to assess the effects of UV-induced free radicals in formulations, i.e. the Radical Potential (RP) Method.
BASF experts created two sunscreen
formulas containing organic UV filters with identical protection in the UV B region (SPF 30) and comparable protection in the UV A spectral range. The amount of UV- inducible free radicals was then assessed for both formulations. In addition, both formulas were tested in a clinical study on subjects with a history of Acne aestivalis, a special kind of polymorphous light eruption. It is reported to occur after sun exposure and is often correlated with sunscreen use, since the affected skin areas are exposed to frequent solar radiation and UV A radiation in particular. The aim of the investigation was to find
a correlation between the amount of UV- inducible free radicals within a sunscreen formulation and the clinical symptoms of A. aestivalis and, potentially, other types of skin reactions. Very different RP values (levels of UV- induced free radicals) and completely
n 10% Almond oil n 0.5% PO “B” n 0.5% PO “A” n 10% Olive oil n Placebo
100 80 60 40 20 0
-20 1 2 3 4 5 6 UV irradiation times, min
Figure 1: Free radical generation in a cosmetic formulation (placebo) spiked with natural oils or perfume oils (PO).
different skin reactivity were obtained where an excellent correlation between the in vitro parameter and the clinical symptoms could be shown. To our knowledge, these are the first ever results to provide direct evidence for a strong
Table 1: INCI of the SPF 30 sunscreen formulas 12-1 and 12-2 INCI
A
Sucrose Polystearate (and) Cetyl Palmitate Disodium Cetearyl Sulfosucchinate Cetearyl Alcohol Lauryl Lactate
C12-C15 Alkyl Benzoate Dibutyl Adipate
Phenoxyethanol (and) Ethylhexylglycerin Ethylhexyl salicylate (EHS)
Butyl methoxydibenzoylmethane (BMDBM) Diethylhexyl butamido triazone (DBT)
Bis-ethylhexyloxyphenol methoxyphenyl triazine (BEMT)
Ethylhexyl triazone (EHT)
Diethylamino Hydroxybenzoyl Hexyl Benzoate (DHHB)
B Aqua Glycerine
Xanthan Gum Disodium EDTA
C Phenylbenzimidazol sulfonic acid (PBSA) Aqua
Tromethamine
D Methylene bis-benzotriazolyl tetramethylbutylphenol (MBBT)
E Undecan, Tridecan November 2018
3.50 2.00
2.00 3.00
3.00
44.60 2.00 0.20 0.20
39.10 2.00 0.20 0.20 2.00 5.00 2.00
2.00
12–1 3.00 1.00 1.00 5.00
10.00 10.00 1.00 5.00
12–2 3.00 1.00 1.00 5.00
10.00 10.00 1.00 5.00 4.00 3.00
2.00 2.50
correlation between UV-inducible free radicals of formulations and the potential to induce A. aestivalis in sensitive subjects. Furthermore, it offers a rationale for the development of low-risk sunscreen formulations by selecting suitable filter systems combined with in-situ ESR analysis.
Radical Potential method A semi-stable spin probe PCA (2,2,5,5- tetramethyl pyrrolidine N-oxyl, 0.01 mM final concentration) was added to the diluted cosmetic product. The samples were inserted in capillary quartz tubes, the concentration of the spin marker was monitored by ESR spectroscopy before and after being subjected to defined UV radiation doses. The PCA spin probe was photostable and resistant to antioxidants, but it promptly reacted with the UV- generated free radicals inside the samples, which were mainly hydroxyl radicals, lipid peroxides and lipidic radicals. The amount of UV-generated free radicals could be quantitatively detected from a calibration curve and the results were expressed as a percentage of UV-inducible free radicals. The UV irradiation of the samples was
performed using a 300-W Oriel UV solar simulator from Newport. The integrated
Table 2: Relative amount of free radicals, N=2 Product
% of induced free radicals UVAB
12-1 12-2
0 ± 0.7 45.3 ± 1.0
% of induced free radicals UVA
0 ± 0,1 21.9 ± 0.2 PERSONAL CARE EUROPE 7 8 9 10
rel. amount free radicals, %
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