SUN CARE In vivo SPF■ In vitro UVAPF■
52 50 48 46 44 42 40 38 36 34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0
Organics only Aqueous TiO2 only Organics + Aqueous TiO2
Figure 2: In vivo SPF values & in vitro UVAPF values of the same three dispersion only and a combination of organic UV filters with
formulations but with different UV filters Organic UV filters only, Aqueous TiO2
aqueous TiO2 dispersion
form yellow coloured complexes when used alongside metal species, i.e. TiO2
41
Figure 3: Increase in the optical pathway of photons in an absorbing medium on account of scattering1
. The yellow
complexation does not actually reduce the UV protection of the filters, but it is undesirable from an aesthetic point of view to have a yellow coloured sunscreen. However, if these two UV filters must
be used together then there are things that can help. A good method would be to use a chelating agent in the formulation to help avoid complexation. It is also recommended to use an organic compatible TiO2
such as grades
with dense silica coatings. This is because silica is selected as having the lowest potential to interact with BMDM.7 In addition, using an aqueous TiO2
dispersion means that there is no interaction with organic UV filters. This allows more optimisation of the oil phase, meaning that you can really take advantage of the formulation synergy. It should, however, be
TABLE 5: FORMULATIONS USING EMULSIFIER E Phase A
Ingredients Aqua
Glycerin Xanthan Gum
Magnesium Aluminium Silicate Aqueous TiO2
B C12-15 Alkyl Benzoate
Decyl Isostearate (and) Isostearyl Isostearate
Glyceryl Stearate (and) PEG-100 Stearate
Sorbitan Stearate Polysorbate 60
C
Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine
Ethylhexyl Salicylate D
Butyl Methoxydibenzoylmethane Octocrylene Preservative
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noted that the combination of BMDM and TiO2 is not permitted in the USA under the current
FDA’s proposed rules for sunscreen products.6 An internal study demonstrated that the is used with BMDM dispersion
yellowing seen when TiO2 is far less when aqueous TiO2
is used compared to the oil-based TiO2 dispersion of the same particle size. This test
was performed using a colorimeter after one day, one week and once month. Figure 4 shows the yellowing results when assessed. The higher the b-value the greater the extent of the yellowing. As Figure 3 shows, there is a clear reduction
in yellowing of a formulation when an aqueous TiO2
dispersion is used alongside BMDM compared to the oil-based TiO2 dispersion.
Again, this is thought to be down to the filters working well together as they are in separate phases of the emulsion.
Conclusion The theory behind synergy is that when organic and inorganic UV filters are combined these UV filters provide two different mechanisms of protection rather than one (if used alone). With an inorganic physical UV filter such as TiO2
, the
mechanism of protection is generated through three mechanisms which are reflection, scattering and absorption of the UV light.5
These inorganic
filters have many advantages such as broad- spectrum protection, photostability and known mildness.
With an organic UV filter, the mechanism of
protection is through a chemical reaction that occurs which is initiated, when UV light hits the UV filter. When this happens conformational molecular changes take place and are then released as both heat energy and radiation of a high wavelength.5 Organic UV filters may have some
disadvantages such as a narrower spectrum
Organic only Up to 100 3.00 0.20 0.80 –
10.00 5.00
3.00 3.00
0.40 2.00 5.00
2.00 8.00 0.80
Organic + Aqueous TiO2 Up to 100 3.00 0.20 0.80 –
10.00 5.00
3.00 3.00
0.40 2.00 5.00
2.00 8.00 0.80
TABLE 6: FORMULATIONS USING EMULSIFIER F Phase A
Ingredients Aqua
Glycerin Xanthan Gum
Magnesium Aluminium Silicate Aqueous TiO2
B C12-15 Alkyl Benzoate
Decyl Isostearate (and) Isostearyl Isostearate
Steareth-2 Steareth-21
C
Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine
Ethylhexyl Salicylate D
Butyl Methoxydibenzoylmethane Octocrylene Preservative
Organic only Up to 100 3.00 0.20 0.80 –
10.00 5.00 2.00
3.00 2.00 5.00
2.00 8.00 0.80
Organic + Aqueous TiO2 Up to 100 3.00 0.20 0.80 –
10.00 5.00 2.00
3.00 2.00 5.00
2.00 8.00 0.80
October 2021 PERSONAL CARE
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