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pH drift in body cream
Hi everyone,
I am formulating a body cream and I like the look, feel, and texture of the final product. But I experienced a drift in pH the very next day. I’ve been looking at buffers and found that sodium citrate and citric acid could help: https://www.newdirections.com.au/100g-Sodium-Citrate
So I tried it in my formulae:
47.95% Water
22.00% Green Tea Butter
7.00% Butylene Glycol
5.00% Yogurt Powder
4.50% Castor oil
4.00% Heliosoft
2.50% IPM
3.00% Fragrance
1.00% Euxyl 9010
1.00% Vitamin E- T50
0.80% NeoDefend [Gluconolactone (and) Sodium Benzoate]
0.22% Sodium Citrate
0.05% Citric Acid
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100.00%
The initial pH via plastic pH strips (I know not as accurate) is 4.5 and the next day it drops to 4.0
Side note: the emulsion stayed stable, no discoloration, tingling, and never dropped its pH again.
So then I adjusted the formulae yesterday to this:
47.95% Water
22.00% Green Tea Butter
7.00% Butylene Glycol
5.00% Yogurt Powder
4.50% Castor oil
4.00% Heliosoft
2.50% IPM
3.00% Fragrance
1.20% Sodium Citrate
1.00% Euxyl 9010
1.00% Vitamin E- T50
0.80% NeoDefend [Gluconolactone (and) Sodium Benzoate]
0.05% Citric Acid
100.00%
This time the initial pH was 5.0 and the next day (today) it dropped to 4.5
Do you think I should keep increasing the sodium citrate or is there an ingredient you think could help anchor the pH? I know that the pH of the skin can range from 4.7-5.7 and I want it to be around a pH 5.5.
Also any books, videos, or websites you think would be helpful are greatly appreciated. I not only want to get help with this formula but want to learn so that I can optimize future formulations.
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3 Replies
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Typically the buffers you are looking at…address pH drifting ‘UP’, not down. I would guess…that you have ingredients that lower the pH, that are not fully in solution/dissolved when you are taking your measurements. You can confirm this….by checking the pH over the next week…and seeing if there is further change.
Try making a version without the Gluconolactone, and see if that does not stop the drift.
Of course…. buy a pH meter. ????
I know you did not ask….but:
Too much Vit E!
Your emulsifier is a weak one….. and you have not surrounded it with any builders! Look at adding a kiss of gum and some fatty alcohol….or I think you will have issues down the road…with shelf life.
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I guess the culprit is NeoDefend (Gluconolactone, Sodium Benzoate). Here are some tips from Lotioncrafter (they sell NeoDefend):
In some formulations, NeoDefend<sup>TM</sup> has been found to cause a pH drift downwards. In such situations, sodium citrate or phosphate buffers can be used to stabilize the pH. Dose the final product with the required level of NeoDefend<sup>TM</sup> along with 1.5x amount of sodium citrate. For example, a 2% dose of NeoDefend<sup>TM</sup> should be accompanied by 3% sodium citrate. Mix thoroughly to ensure all solids have dissolved and adjust the pH of the formulation to 7.00 - 7.25 with 30% sodium hydroxide. Finally, adjust the pH to desired final product pH (pH 5.4 – 5.5 is ideal) with dilute sodium hydroxide or citric acid solution.
In fact, these recommendations have been taken from one of Lonza’s docs for Geogard Ultra (same INCI as NeoDefend). There is a bit more detailed info on the last page of another Lonza’s guide:
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Not sure what the purpose was of adding the product with Gluconolactone was? I had assumed it was to serve as your chelate? Why not just make life easy….and add something like: GLDA, aka TSGD aka Tetrasodium Glutamate Diacetate.
Seems like you have created a great deal of hassle….which could easily be eliminated by this simple drop in?
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