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2 SPF pr % “invisible” Zinc Oxide only achievable?
Could you make a 15% ZnO SPF30 sunscreen without using any other sunscreen actives? It’s much easier adding TiO2 as you can get to 3 SPF pr % mineral, but say you want ZnO only.
Say you start at 1 SPF pr 1% ZnO, critical wavelength 371 nm.
5% Butyloctyl Salicylate + 40 %
2% Ethylhexyl Methoxycrylene + 15%What would you add to then take it to 2% in vivo?
Silane coating?
Film formers?
Acrylate beads?
Bisabolol
Tocopherolhttps://knowledge.ulprospector.com/9102/pcc-spf-boosting-technologies-tips/
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4 Replies
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To be able to state a certain SPF figure on the label, expensive testing is needed.
Sunscreens are totally out of reach of small companies and home formulators.1 First you’d need to know how much UV rays can ZnO and TiO2 absorb
As TiO2 is more effective in UVB and ZnO in the UVA range, the combination of these particles assures a broad-band UV protection.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3781714/Particle size greatly influences UV absoption
However, to solve the cosmetic drawback of these opaque sunscreens, microsized TiO2 and ZnO have been increasingly replaced by TiO2 and ZnO nanoparticles (NPs) (<100 nm). This review focuses on significant effects on the UV attenuation of sunscreens when microsized TiO2 and ZnO particles are replaced by NPs and evaluates physicochemical aspects that affect effectiveness and safety of NP sunscreens. With the use of TiO2 and ZnO NPs, the undesired opaqueness disappears but the required balance between UVA and UVB protection can be altered. Utilization of mixtures of micro- and nanosized ZnO dispersions and nanosized TiO2 particles may improve this situation.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3781714/https://www.sciencedirect.com/science/article/pii/S13
2 Then you need to know how much of these particles remain on the skin to block UV rays.
3 Then you need to make sure they are safe.
SafetyThe International Agency for Research on Cancer (IARC) has recently classified TiO2 as an IARC group 2B carcinogen, possibly carcinogenic to humans.60,61 The IARC conclusions are based on evidence showing that high concentrations of pigment-grade and ultrafine TiO2 dust cause respiratory tract cancer in rats. The IARC considered the observations as relevant to humans since some biological events that cause lung cancers in the rats appear to be similar to those seen in humans working in a dusty environment.Skin penetration
Although in-vitro animal skin penetration studies mainly report TiO2 and ZnO NP localization within the SC and/or hair follicles, some in-vivo studies have detected the NPs in viable skin layers.85,86 Sadrieh et al, for instance, showed that repeated application of 5% TiO2 (uncoated and coated particles, ~20–500 nm) sunscreen formulations on the skin of Yucatan mini-pigs led to detectable levels of the particles in the dermis.Their in-vitro porcine skin penetration studies revealed no TiO2 NP penetration, but in-vivo experiments with hairless mice resulted after 30 days penetration of 4 and 60 nm particles (5% TiO2 in carbopol 940, triethanolamine and demineralized water) into deeper viable epidermal layers. After another 30 days, the particles were allocated in various tissues such as lung (12–18 μg g−1 Degussa P-25), brain (10–15 μg g−1 Degussa P-25) and spleen (22–30 μg g−1 10 nm particles). It should be noted that the ability of TiO2 particles to cross the blood–brain barrier had been previously published.87
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3781714/Just the SPF testing will cost 5 figures itself.
Bottomline don’t even attempt to formulate or sell anything claiming a SPF figure yourself. -
if by sunscreen actives you mean additional UV filters, then the answer is no -
@gunther I appreciate your concern, but already done with one round of in-vivo SPF testing. It is however very true that it’s expensive to keep doing in-vivio test which AFAIK there is no substitute for with mineral sunscreens (with organics you can get comparable results in vitro).
@Bill_Toge I think the answer might be yes, Kobo claims that they’ve achieved 6.17 SPF pr % mineral (TiO2 + ZnO), so it might be possible to get to 3 with ZnO only.
Sunscreen actives
TiO2 (40 nm) 3.54%ZnO (265 nm) 7.15%
Antioxidant/ Anti-inflammatory
Booster blend ATB 5.00% (Argan Oil, Tocopherol, Bisabolol)UV absorber/StabilizerEthylhexyl Methoxycrylene 1.37% (Boosts PFA, might protect from mineral tox)Butyloctyl salicyalte 4.48%Film former
Acrylates copolymer 1.5%Index Value SPF 66Estimated value without boosters SPF 15 - 20PFA 21 Estimated PFA without boosters 5CW (nm) 380 -
It might be a little off topic, but you may want to look at the AppleChem GBlock line. It is fairly easy to work with and they do have an SPF calculator (spreadsheet) that gives you a “close” approximation of final SPF and Spectrum. They have some great documentation available on their website. https://www.applechem.com/
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