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Formulating a sunscreen lotion with mineral UV filters.
Hi,
I
want to make a sunscreen lotion without other actives than the UV filters, for
own use. The SPF will be about 15. The UV filters I use are micron. zinc- and
titanium(di)oxide, coated with simethicone (SofiTix).I also want to add another, volatile silicone, because of its nice skinfeel. I
know silicones can be tricky, so I hope the stability of the way I formulated
etc will be sufficient. This is the first time I will be working with
silicones.My formula, feel free to comment, much appreciated!
·
q.s.
deionized water·
8%
E-wax (glyceryl stearate + PEG100 stearate)·
2%
cetyl alcohol·
1%
cyclopentasiloxane·
9%
sunflower seed oil·
1%
petrolatum·
1.5%
glycerin·
0.5%
α-tocopherol·
6% SofiTix (nano zincoxide/nano
titaniumdioxide/simethicone)·
0.4% phenoxyethanol·
0.3% benzyl alcohol + DHA (Cosgard)·
0.1% potassium sorbate·
citric
acid in aqua for pH < 5.5Phase 1:
Disperse SofiTix in mixture of sunflower oil + cyclo D5
Phase
2:
Water +
glycerin, heat to 70CPhase
3:
Melt the
emulsifiers + petrolatum -> 70CAdd
phase 1 to the 2+3 emulsion in the cooling phase.
Add
preservatives + α-tocopherol.QUERY: Would 9% oil be enough
to disperse 6% SofiTix?If so, should I use even less oil in the premix and add oil to phase 3?
Would this be stable enough for the 1% cycloD5 and the simethicone coating?
I wanted to add benzyl alcohol to prevent discoloration by potassium sorbate,
like @DRBOB@VERDIENT.BIZ said. I don’t use it very long, so it probably won’t
be necessary.Is pH 5.5 low enough for potassium sorbate to ‘metabolize’ into sorbic acid?
Thanks a bunch!
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9 Replies
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yes 9% oil should be enough to dispese 6% Sofitix.Also 5.5 in low enough to form sorbic acid from Ksorbate which should be fine for preservation but will discolor with time however you use it up quickly.Why don’t you raise Ph to 7-7.5 for optimum stability of Zn O and just use either BA or phenoxyethanol at ! % ?
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@DRBOB@VERDIENT.BIZ
I didn’t know the optimum stability of ZnO being so high? And what about the TiO2?
Will it really be a problem to put it at 5.5? If it is necessary, I’ll raise the pH with Na lactate and get rid of the phenoxy and potassium sorbate (which isn’t stable then I assume) and just do the Cosgard (BA +DHA).
Or just phenoxyethanol alone?
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Below 7 Zno forms Zn++ ions which raises issues of stability/efficacy so we always keep our mineral sunscreens above 7: At 7 K sorbate doesn’t work but you can use either BA or Phenoxyethanol at 1%.
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Edit: message deleted, question is answered above.
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@DRBOB@VERDIENT.BIZ
At 7 K sorbate doesn’t work but you can use either BA or Phenoxyethanol at 1%.
Does that mean I don’t need additional antifungal excipients at pH7 or >7?
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no you should be fine
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@zwapp
Thanks for the reminder, you’re right! I’ve got tocopherol acetate aswell, so that’s not a problem. Or I just leave it out, both. -
I have heard if titanium di oxide is inhaled during preparation it may be carcinogenic itself.
So does it necessary to use in spf lotion
Or what is the safe method of handling tio2. -
@pradeep
Lots of chemicals have inhaling hazards, even cellulose or niacinamide. Take adequate safety measures all the time (ventilation etc). If you handle powders a lot, you can think of using simple dust-masks.For this lotion I have chosen a combination of TiO2 and ZnO, both are broad spectrum.
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