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Cosmetic Cream measuring the pH
I would like to be able to adjust my skin cream to a 5.0 pH with either citric acid or sodium bicarbonate which I understand are the approved ingredients to use.
My question is the method that I should use to read the pH. In the case of liquid soap I would dissolve a known amount soap with a known amount of distilled water and use that as the control standard. I would then make the adjustments in accordance with the control.
Given that there are oils in a skin cream is it necessary to take the oil component into account, if so how? Or can I safely ignore the oil content which is usually less than 20%?
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20 Replies
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You use a pH meter to measure the cream. That’s it. When you refer to “liquid soap” if you mean soap made by saponifying oils, there is no agreed method of measuring the pH, in general the “zap test” is used (tasting it). Provided you calculate the weights correctly using a soap calculator and the process goes OK there should be no problem.
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Thank you, I had suspected this was the case but I thought there might be a method of using a “control” to adjust where necessary. I aim for 4.5 to 5.5 for creams aimed at my clients of advanced years and 5.0 to 6.0 for the younger generation.
Cheers
Mac -
Sure, no problem. In practice I find that the majority of creams with the exception of carbomer types, tend to naturally be in the desired range and need little or no adjustment.
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Yes correct-to measure pH of a product-use a pH-meter. If you have to dilute your cream to be able to make a measurement, you can’t claim your cream has a certain pH - only the dilution of it.
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we just make a series and record the measurements. So .5%, .6% .7% that way you can see where your cutoff is in terms of viscosity and stability.
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Thank you gentlemen. I am most happy to accept your advice. Is there also a place for using test strips? If so is there a type/brand that you would recommend?
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Test strips. Yes. I often use test strips, usually during prototyping work. These come, generally speaking, in four types:
1. Litmus. Good for testing the crossing point at pH neutral, but useless otherwise.
2. General purpose low cost. These are usually a sort of mustard colour and turn different colours according to pH. Not very accurate in my opinion but can be useful as a low cost option in early experimental work.
3. Wide range 5-pad strips. A lot more pricey, these are plastic strips with 5 small pads of colour material stuck to them. You interpret the pH according to the colour combo. In my opinion these are pretty accurate, certainly to plus or minus 0.5
4. Similar to (3) but with just two pads, the 5.5 - 8.5 strip. This is more accurate than item 3, when you know that you’re working within that pH range. Can generally be interpreted to plus or minus 0.25 -
Thank you again. I am getting very close to joining Mr. Romanowski’s classes. I am encouraged by the thought that I know just enough to know that I know very little. I am sure I am never going to be too old to learn, so back to school very soon.
Cheers,
Mac -
RE: Wide range 5-pad strips. A lot more pricey, these are plastic strips with 5 small pads of colour material stuck to them. You interpret the pH according to the colour combo. In my opinion these are pretty accurate, certainly to plus or minus 0.54. Similar to (3) but with just two pads, the 5.5 - 8.5 strip. This is more accurate than item 3, when you know that you’re working within that pH range. Can generally be interpreted to plus or minus 0.25
I need a pH reading up to .0 for my facial creams. I’ve been researching the less expensive meters and the companies that makes them, reading endless reviews on Amazon etc. Do you have a suggestion for a cost effective waterproof meter or would the wide range 5-pad strips be the best way to go. Many people complain about the meters not working, (Oakton), batteries being expensive, replacement parts, one year warranty only (which seems to be the time the meters break) and bad customer service. Im talking about the 75 to 100 dollar range meters.
And if I did end up getting the 5-pad strips as a best option, could you suggest where would be a good place to get them?
Thanks!!
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Amazon, eBay (Lab supplies) etc. sell pH testing strips of several types.
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If you’re serious about formulating, get a pH meter. Strips are practically useless.
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Hi. I’m not trying to hyjack this post but I’m UK based and I’ve been trying to find a ph meter that will work in creams, lotions, scrubs and body washes. I’ve mainly come across ph meters for measuring water samples (ponds, fish tanks etc). I’m assuming they wouldn’t be useful for creams? I’ve looked up a company that manufacture ph meters but the price range is from £37 to well over £500, as I’m learning and by no means a qualified chemist or scientist I’m becoming confused as to what I need. I purchased the strips with the plastic backing and foam pads and IMHO they’re a complete waste of time and money. Would anyone be able to point me in the right direction please? (I’ve been looking at Hanna Instrumemts products by the way)
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Get a Hanna portable pH meter … will work for any purpose. I mean … pH is pH … there nothing magical about it whether it’s a cream, lotion, body wash.
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Avoid using a glass electrode pH probe in solutions of cationic surfactants. It can happen that the surfactant can deposit on the surface of the very thin glass of the electrode and thus wreck it.
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Thank so much for the advice.
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When I measure pH of creams, I stick the pH electrode in the cream, even if the cream is thick, and move it gently. Is the pH measured this way reliable? Am I doing it right?
I read somewhere that in thick creams it is difficult for the ions to migrate to the electrodes and therefore the pH reading cannot be reliable. The suggested method was to dilute 10% of cream in distilled water. However, this confuses me because with addition of water, I think the pH will change and be different from the pH we want to measure (that of the cream).So what is the right way to measure pH in thick creams? Any thought?
Thank you!
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AnnalisaB said:When I measure pH of creams, I stick the pH electrode in the cream, even if the cream is thick, and move it gently. Is the pH measured this way reliable? Am I doing it right?
I read somewhere that in thick creams it is difficult for the ions to migrate to the electrodes and therefore the pH reading cannot be reliable. The suggested method was to dilute 10% of cream in distilled water. However, this confuses me because with addition of water, I think the pH will change and be different from the pH we want to measure (that of the cream).So what is the right way to measure pH in thick creams? Any thought?
Thank you!
I honestly would like if anyone has answers to this. I feel the samevway
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Dilution of a factor 10 with distilled water will not affect pH (scientifically, it does but the deviation is so small, it doesn’t matter in practice) and is hence a valid tool to measure pH in thick creams or w/o emulsions or hard products such as soap.Strong dilutions will show a pH shift which is usually in the zero point something range. Effects of temperature on pH are about as strong/weak and therefore, dilution commonly won’t show noticeable effects in everyday life.Pure water has a pH of 7 which is due to self-dissociation into equal parts of hydronium and hydroxide ions. Once there are even small quantities of pH active substances dissolved in said water, pH reading will reflect pH of aforementioned substances and no longer water. -
Are there any ISO methods or pharamcopeiae regarding measuring pH of creams, especially Water-in-Oil emulsions? Diluting isn’t always possible, even if it is accurate. I’ve seen some say dilute 10% in water, some “stick it in the cream”, some dilute in hot alcohol, etc.
Is there anything official or peer-reviewed? -
I don’t know by heart, I would have to look it up in a pharmacopoeia (you may drop by at my work place any time)… or you go to a pharmacy near you and ask there
.With o/w creams of lower viscosity, direct measurement is accurate and feasible. Slight dilution like 10x will give a negligibly different pH (good enough for cosmetics) and may be preferred in lamellar emulsions aka liquid crystal networks or when dealing with unknown or mixed type emulsions.In w/o emulsions, sufficient dilution is mandatory. You have to add enough water to break the emulsion and centrifuge if needed (which is also a cleaner approach because no oils sticking to the electrode).Alcohol, though it has ‘no measurable pH’, is not optimal because it can actually change the pH in some formulations like such containing free fatty acids or poorly water but alcohol soluble pH active ingredients (ferulic acid comes to mind).
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