Niacinamide/NAG/Resveratrol combo oxidising

KBoel

Hello everyone. 
My first post here. 
Over the past year I've been experimenting with creams, lotions and serums. I like to combine niacinamide, n-acetyl glucosamine, and resveratrol, as I find they compliment eachother well in efficiency. However, each time, whether it's a cream or serum, the color of the product changes into something much darker over the course of several weeks. I've narrowed it down to these 3 being the culprit, as all the other ingredients are different in each formulation.
I've been searching the net for an explanation, but can't seem to find anything.
Can anyone explain why this phenomonon occurs, or link me to any information? Many thanks for your time.
Regards, Kat.

ngarayeva001

I made many moisturisers with NAG and Niacinamide (O/W and W/O, different oil phase, different emulsifiers) and they don't oxidise. I am pretty sure it's resveratrol. Are you using a powder or a version solubilised in PG?

Pharma

What's the pH of your formulas and are they stocked in transparent containers? Resveratrol is fairly unstable at neutral to alkaline pH and sensitive to light.

As @ngarayeva001 mentioned, NAG and niacinamide are more stable and don't readily oxidise.

ngarayeva001

I don’t know why is it happening but the experience I have with antioxidants so far, they cause oxidation rather than prevent it. I have this issue with ubiquinone, resveratrol and tetrahexyldecyl ascorbate which is an oil soluble derivative and claimed to be stable.. I know that some might say it’s anecdotal evidence and those are perfectly good ingredients but I heard the same from other people. Maybe I am doing something wrong with all these antioxidants. 

ngarayeva001

I either don’t use vegetable oils or make sure those are not high in polyunsaturated fats. I add BHT and tocopherol. I don’t use any sort of botanical extract. They still oxidize.

Pharma

Tetrahexyldecyl ascorbate is kind of astonishing but for the rest: antioxidants are meant to reduce other substances and become oxidised themselves instead, it's what they do. The trick is to start with something that doesn't require reduction i.e. which isn't already oxidised. If it still happens: get rid of oxygen. This can be done by mixing in vacuum and/or by using degassed water (one of the handy things you can do with an ultrasound bath). Furthermore, but I suppose this is already the case, avoid alkaline pH.

Ubiquinone can be reduced by ascorbic acid and likely by BHT, the resulting ubiquinol is very readily going to oxidise back. It's also slightly reactive to nucleophiles such as free -SH and some -NH2 groups (especially the former is a rather unlikely case in cosmetics).

ngarayeva001

I made this in late June. A simple moisturizer with 10% of tetrahexyldecyl ascorbate. I don’t have a formula in front of me now, but there’s nothing suspicious in it. Only non prone to oxidation esters, some dimethicone, chelators, antioxidants (BHT, tocopherol), emulsified with arlacel 165 and 0.3% of Sepimax Zen, preserved with parabens. I am subscribed to several Facebook formulation groups, and remember 6-7 people complaining that it happened to them as well. If this is not a typical reaction the only thing that comes to my mind that there might be something wrong with the material sold on DIY market (repackers). Maybe they don’t store it properly or something.. 

Bill_Toge

how much BHT and tocopherol are you using?

might be worth using a water-soluble antioxidant (e.g. sodium metabisulphite) as well

ngarayeva001

0.1% of each tocopherol and BHT. I will have a look what water-soluble antioxidants I can find.

Pharma

Metabisulphite, if allowed in cosmetics (dunno, really no idea) and if not concerned about it allergic potential, is great since it reacts with oxygen and turns your product oxygen free = pretty darn stable regarding degradation of antioxidants.

Bill_Toge

@ngarayeva001 try increasing the BHT to 0.5% and the tocopherol to 5%; there's an awful lot of vitamin C equivalent in there, and 0.1% of either won't last long against its insatiable lust for oxygen

@Pharma sodium metabisulphite is permitted, albeit restricted, in Europe as a preservative at up to 0.59% (Annex V/9), and at higher levels in oxidative hair dyes, hair straighteners and self-tanning products (Annex III/99)

ngarayeva001

Thank you @Bill_Toge, I will try to increase both and see what happens. I had a perception that these antioxidants are supposed to be used at a low level (both suppliers recommendations and information from the forum)