Hydroquinone cream changes color (antioxidants?)

Hi Guys,

I need some advice with my 2% Hydroquinone cream. I made it two weeks ago and noticed it changes colour (gets darker). It is in a clear bottle but I in a dark cabinet. I keep it in a clear PET bottle intentionally to observe whether it is going to change or not. Maybe I should increase antioxidants (use different antioxidants)? Any input is appreciated:

INCI %

A Aqua 61.10%

A Glycolic acid 6.00%

A Butylene Glycol 3.00%

A Betaine 2.00%

A Disodium EDTA 0.20%

B Butylene Glycol ester 10.00%

B Cetearyl Isonononoate 5.00%

B Dimethicone 1.50%

B Cetyl Alcohol 3.00%

B BHT 0.10%

B Glyceryl Stearate/PEG-100 Stearate 3.00%

B Sepinov EMT 10 0.50%

C Germaben II 1.00%

C Hydroquinone 2.00%

C Allantoin 0.50%

C A- Bisabolol 0.10%

C TEA 0.50% (approx)

C Tocopherol 0.50%

pH is between 4.5 and 5 (my meter acts funny)

Anticipating some comments I am giving a disclaimer: it is just 2%, it is for personal use only and I am not going to share it with anyone. I know it's a serious ingredient, but I have a couple of annoying freckles and sunspots but as you all know alfa arbutin/niacinamide/NAG, vitamin C and other fancy ingredient's don't work. 

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Comments

  • PharmaPharma Member, Pharmacist
    Hydroquinone has a lower redox potential than tocopherol and BHT: These two may protect hydroquinone (especially BHT since it's more reactive and gives a more stable radical) but they do not regenerate built benzoquinone. This means, if they catch oxygen or other oxidants before these react with hydroquinone, they help. Alas, regeneration is more important since bezoquinone, the oxidised form of hydroquinone, quickly reacts to form those brown pigments. Also, BHT and tocopherol usually undergo one electron redox reactions (= build stable radicals) whereas hydroquinone <-> benzoquinone is a two electron redox reaction. Ascorbic acid is your friend! It has a lower redox potential = recycles benzoquinone back to hydroquinone and does a two electron reaction too. An alternative and/or addition to ascorbic acid would be sodium metabisulfite (which is of great advantage since it can catch oxygen from your product and thereby remove the root of all evil).
  • Thank you @Pharma. I might be missing something, but as per my experience with LAA, it oxidises in the presence of water itself.  Is it somehow different with these type of formulas?
    I was lucky to find sodium metabisulfite on amazon. It's for use in wine, I wonder if it's ok for cosmetic use? 

  • PharmaPharma Member, Pharmacist
    There's usually an abundance of air e.g. oxygen dissolved in water. LAA does react with it but it's not very efficient compared to metabisulfite (which is safe if you're not allergic to sulfite and allowed at low concentration in cosmetics -> forgot how low).
  • I saw a couple pf formulas (one with hydroquinone) where it was used at 0.2%
  • sodium metabisulfite perfectly work as @Pharma said. even in 4% hydroquinone cream. (not cosmetic). 
  • Thank you. I have already ordered it and will try it.
  • You can also consider a low pH to help hydroquinone stability

    The conventional pH for hydroquinone topical formulations is preferably acidic, and generally below or close to a pH of 4, even though this can be harsh to the skin and possibly other components of the product. Hydroquinone is more stable, and less likely to discolour under acidic conditions. Variations in pH have been shown to result in marked discoloration [5,15]
    https://www.researchgate.net/publication/332214383_Tuning_the_Transdermal_Delivery_of_Hydroquinone_upon_Formulation_with_Novel_Permeation_Enhancers
    (You can download the full PDF by clicking on the 'Download full-text PDF' blue box on the upper righthand corner)

    I wonder if Sodium metabisulfite is stable at relatively low pH levels
    but likely it is as it's used in some acidic beverages.
  • Thank you @Gunther, it’s very useful. I know sodium metabisulfite is used in wine which I assume is rather acidic. I will decrease the pH below 4.
  • This study shows that despite using Na-metabisulfite, undegraded hydroquinone will still drop to < 50% in 12 weeks
    So Sodium metabisulfite is no silver bullet, albeit the cream pH ain't mentioned in the study at all.
    http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.584.6620&rep=rep1&type=pdf

    So it looks like you'll need to Google more hydroquinone cream stability studies and patents before you keep on formulating.
    Please keep us posted on your findings.
  • What I found so far, is some information on that it’s more effective at alkaline pH. But I would rather keep it stable.
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