Meeting the UVA Challenge: Inorganic-only Sun Protection

Sep 1, 2010 | Contact Author | By: Paul Staniland, PhD, and Julian P. Hewitt; Croda Sun Care and Biopolymers
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Title: Meeting the UVA Challenge: Inorganic-only Sun Protection
titanium dioxidex UVA protection factorx SPFx UVA/UVB ratiox
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Keywords: titanium dioxide | UVA protection factor | SPF | UVA/UVB ratio

Abstract: The production of a range of titanium dioxide-based dispersions is explored to provide enhanced UVA protection, in comparison with ultrafine titanium dioxide. Formulations containing these dispersions as the only active are shown to achieve a UVA protection factor that is 1/3 of the labeled SPF value, thus meeting European Commission recommendations.

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P Staniland and JP Hewitt, Meeting the UVA challenge: Inorganic-only sun protection, Cosm & Toil 125(9) 32-40 (Sep 2010)

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Ultraviolet A (UVA) radiation accounts for 95% of the total UV radiation reaching the earth’s surface and covers a wavelength range from 320 nm to 400 nm —the longest UV wavelength. UVA can penetrate though the stratum corneum to the epidermis and dermis and stimulate tanning and pigmentation, as well as cause skin aging. Although UVB is more immediately damaging to the skin than UVA, it is now recognized that sunscreen products should protect against UVA as well as UVB.

While most existing sunscreen products provide good protection against UVB, leading dermatologists have voiced concern over the lack of UVA protection offered by current sun care products. In addition, recent publications by Draelos et al. and Murphy et al. have pointed out the importance of good UVA protection in the management of photodermatoses and prevention of skin cancer.

However, optimizing the UVA performance of sunscreens is challenging, particularly for global markets since UVA performance and labeling requirements differ from one region to another, some being more difficult to meet. Consequently, sunscreen manufacturers are finding it necessary to re-formulate products to enhance UVA efficacy while maintaining a high sun protection factor (SPF).


Lab Practical: Enhanced TiO2 Dispersions

  • All formulations incorporating the enhanced UVA TiO2 dispersions passed European guidelines for UVA protection.
  • Enhanced UVA TiO2 dispersions showed reliable performance across a range of formulation systems.
  • W/O emulsions using the enhanced UVA TiO2 tended to provide slightly higher SPF efficacy than o/w emulsions.
  • SPF units increased in an approximately linear relationship to solids content; each 1% solids enhanced UVA TiO2 typically provided at least 2–3 SPF units.

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Table 1. Test formulas

Table 1. Test formulas

Test formulas prepared from enhanced UVA TiO2 dispersions

Figure 1. UV and visible attenuation profiles

Figure 1. UV and visible attenuation profiles

UV and visible attenuation profiles comparing UVA attenuation of enhanced UVA TiO2 with a standard commercial grade

Figure 2. Cumulative particle size distributions

Figure 2. Cumulative particle size distributions

Cumulative particle size distributions for conventional TiO2 and enhanced UVA TiO2; the curve for the conventional grade shows a broad tail of large particles, which leads to excessive whitening in formulations.

Figure 3. Photogreying index

Figure 3. Photogreying index

Photogreying index for enhanced UVA TiO2, compared with five commercially available grades

Figure 4. In vitro SPF vs. TiO2 active loading

Figure 4. In vitro SPF vs. TiO<sub>2</sub> active loading

In vitro SPF vs. TiO2 active loading for formulations containing the enhanced UVA TiO2 dispersed in C12-15 alkyl benzoate (AB dispersion) and caprylic/capric triglyceride (TG dispersion)

Figure 5. Critical wavelength values

Figure 5. Critical wavelength values

Critical wavelength values for formulations containing various TiO2 products

Footnotes [Staniland 125(9)]

a Solaveil XT-100 (INCI: Titanium Dioxide (and) C12-15 Alkyl Benzoate (and) Polyhydroxystearic Acid (and) Stearic Acid (and) Alumina) and Solaveil XT-300 (INCI: Titanium Dioxide (and) Caprylic/Capric Triglyceride (and) Polyhydroxystearic Acid (and) Stearic Acid (and) Alumina) are products of Croda.

b The Lambda II UV Spectrophotometer used for this study is manufactured by Perkin Elmer.

c The X-ray Disc Centrifuge used for this study is manufactured by Brookhaven Instruments Corp.

d In vitro SPF values were measured using a UV-2000S analyzer (Labsphere, North Sutton, NH), with PMMA plates (Helioplates grade HD6, Helioscience, France) as the substrate.

Formula 1. SPF 20 sun lotion

A.
Xanthan Gum (Keltrol RD, S. Black), 0.10% w/w

B.
Water (aqua), qs

C.
Propylene Glycol, 4.00

D.
Glyceryl Stearate (and) PEG-100 Stearate (Arlacel 165 FL, Croda), 6.00
Sorbitan Stearate (Span 60, Croda), 0.50
Polysorbate-60 (Tween 60, Croda), 2.70
Cetearyl Alcohol (Crodacol C S90 EP, Croda), 1.00
Paraffinum Liquidum (Mineral) Oil, 8.00
Ethylhexyl Palmitate (Crodamol OP, Croda), 2.50
Polydimethylsiloxane (Dow Corning 200 Fluid, 350 cst, Dow Corning), 2.00
VP/Eicosene Copolymer (Unimer U-15, Induchem), 1.00

E.
Titanium Dioxide (and) C12-15 Alkyl Benzoate (and) Polyhydroxystearic Acid (and) Stearic Acid (and) Alumina (Solaveil XT-100, Croda), 18.00

F.
Preservative, qs

Procedure: Disperse A into B. Add C to AB and heat to 75–80°C. Separately heat D to 75–80°C. Add E to D with stirring and maintain temperature. Add DE to ABC with intensive stirring. Homogenize for 2 min. Stir and cool to RT, adding F to batch below 40°C. Appearance = white lotion; viscosity = 12,360 mPas (Brookfield RVDV1, spindle 4, 5 rpm, 1 min); in vivo SPF = 24; UVA/UVB ratio = 0.79; label SPF = 20; in vitro UVAPF = 8; ratio label SPF UVAPF = 2.5.

Formula 2. SPF 30 sun lotion

A.
PEG-30 Dipolyhydroxystearate (Cithrol DPHS, Croda), 2.50% w/w
C12-15 Alkyl Benzoate (Crodamol AB, Croda), 13.00
Isohexadecane (Arlamol HD, Croda), 3.00
PPG-15 Stearyl Ether (Arlamol PS15E, Croda), 1.00
Cyclopentasiloxane (Dow Corning 245 Fluid, Dow Corning), 2.00

B.
Titanium Dioxide (and) C12-15 Alkyl Benzoate (and) Polyhydroxystearic Acid (and) Stearic Acid (and) Alumina (Solaveil XT-100, Croda), 18.00

C.
Water (aqua), qs
Magnesium Sulfate Heptahydrate, 0.80
Glycerin, 4.50

D. Preservative, qs

Procedure: Combine A and heat to 85°C. Separately combine C and heat to 85°C. Add B to A with stirring and maintain temperature. Add C to AB slowly with intensive stirring. Homogenize for 1 min. Stir and cool to RT, adding D to batch below 40°C. Appearance = white lotion; viscosity = 9,540 mPas (Brookfield RVDV1, spindle 3, 5 rpm, 1 min); in vivo SPF = 31; UVA/UVB ratio = 0.79; label SPF = 30; in vitro UVAPF = 10; ratio label SPF/UVAPF = 3.0.

Formula 3. SPF 30 natural sun lotion

A.
Polyglyceryl-3 Polyricinoleate (Cithrol PG3PR, Croda), 3.00% w/w
Bertholletia Excelsa Nut Oil (Crodamazon Castanha do Brazil, Croda), 4.00
Cetearyl Ethylhexanoate (and) Isopropyl Myristate (Crodamol CAP, Croda), 8.00
Squalane (Pripure 3759, Croda), 3.00
Ethylhexyl Palmitate (Crodamol OP, Croda), 2.00
Euphorbia Cerifera (Candelilla) Wax, 1.50

B.
Titanium Dioxide (and) Caprylic/Capric Triglyceride (and) Polyhydroxystearic Acid (and) Stearic Acid (and) Alumina (Solaveil XT-300, Croda), 20.00

C.
Water (aqua), qs
Magnesium Sulfate Heptahydrate, 0.70
Glycerin (Pricerine, Croda), 4.00

D.
Preservative, qs

Procedure: Combine A and heat to 85°C. Combine C and heat to 85°C. Add B to A with stirring and maintain temperature. Add C to AB slowly with intensive stirring. Homogenize for 1 min. Stir and cool to RT adding D below 40°C. Appearance = white lotion; viscosity = 24,300 mPas (Brookfield RVDV1, spindle 5, 5 rpm, 1 min); in vivo SPF = 39; UVA/UVB ratio = 0.63; label SPF = 30; in vitro UVAPF = 10; ratio label SPF/UVAPF = 3.0.

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