[Mayday]

Was the serial dilution test performed on agar plates but the suspension test performed in vials? I see the microbe concentration was equalized to 10 cfu/ml.

If on culture plates, could the medium be providing some level of structural protection from the formaldehyde? Like how HPMC/MC/CMC can reduce effectiveness of Phenoxyethanol by shielding (particularly over 0.5%). Or PEG-4000 and methylparaben.

[Mayday]

Abdullah said:
[…]Sodium phytate is expensive and i am selling low price products.

Considering citric acid is cheap and you already have it in your formula, have you considered chelating with it? Would have to adjust pH down, but it sounds possible. And IDK how it would fare compared to dEDTA.

[Mayday]

@Hanson25 I don’t know really know anything about surfactant interactions, but the sodium cocoamphoacecate may be it because it’s amphoteric and you say the viscosity is changing with pH.

https://www.humblebeeandme.com/project/sodium-cocoamphoacetate/

[Mayday]

What’s your list of INCI ingredients?

[Mayday]

(On second thought that may actually be the NaBenz)

[Mayday]

@Abdullah Warning that sodium phytate will probably need more pH adjustment then disodium EDTA. At 0.05% NaPhy, 0.35% NaBenz, I needed 0.20% citrate to get to pH 4.4 from 10.9

[Mayday]

Thanks Phil and Mark for the advice!

Btw I just realized my usage of ppm at the top is nonstandard. I thought ppm was on a molar basis (ratio of molecules), but it is conventionally calculated by mass.

[Mayday]

Abdullah said:

So what is causing tetrasodium EDTA not chelate iron at pH 4? 

Hi again @Abdullah ????

I can’t answer the chemistry question, but I have found a reference to the fact that each EDTA has their own pH at a standard 5% aqueous solution. They referenced the British Pharmacopoiea, which I do not have access to currently. My guess is that the pH of the EDTA corresponds to the pH range it is effective in.

I could be wrong, but the range for tEDTA (8.5-10) tracks with how I’ve seen it recommended for use in alkaline solutions, soaps, etc. So for yours you should use Disodium EDTA. Can also consider Sodium Phytate or Tetrasodium Glutamate Diacetate, as I believe those are effective at low pH.

[Mayday]

justaerin said:

Unfortunately, it still has a noticable fishy smell at 0.5%. The downside of glucomannan/konjac is the smell, very like BTMS but more tenacious. Maybe since the last time I bought it processing has gotten to the point of removing the fishy smell from the konjac sold as food grade, or maybe I’m just unusually sensitive to it.

Now might be using a different supplier by now, so it isn’t a terribly fair test. Modernist Pantry might be using a clearer or less smelly grade than Now, but I haven’t tried it.

When I contacted Modernist Pantry, they said that their Xanthan and Konjac produce a transparent solution at 0.5% (though I have not verified it). I think Konjac has a tendency to be somewhat fishy, as I recall some people complaining on reddit about zero-carb shirataki noodles being fishy… but for all I know they were making noodles with the Now foods glucomannan. However, it’s possible that Modernist Pantry has a more clarified grade. I’ll try out theirs once I get the chance.

[Mayday]

Abdullah said:

After chemical exfoliant (lactic acid or glycolic acid), how many days minimum and maximum will the inflammation last?

I mean if i am applying 10% lactic acid Evey night, does it mean my face is always in inflammation? 

If true I am curious if that sort of inflammation could also be systemically bad for you, like the link between gum disease and heart disease. Skin surface is massive.

[Mayday]

Abdullah said:

Sodium benzoate+phenoxyethanol is a good combination. I would add 0.1% caprylyl Glycol it it instead of EHG. It is cheaper and more water soluble and almost same effective.

@Abdullah I only mentioned the EHG because it’s a component of Euxyl PE 9010, which I wanted to try out. What do you like to use Caprylyl glycol for? As part of preservative system or for some other affect?

wrt EHG and Euxyl PE 9010, reading the CIR safety assessments for EHG, I think I’ll just stay away from it unless I can make a good case for it. I’m not liking the higher potential for ocular irritation.

Something interesting in the Phenoxyethanol safety assessment:

Treatment with Phenoxyethanol also caused increased permeability of cellular membranes to potassium ions.

So I wonder if Potassium Benzoate may be a better choice to combine with Phenoxyethanol since it’ll increase the potassium ions floating around slightly. But since that’s not widely available, Potassium Sorbate could be the better choice. Or just add a dash of KCl…

[Mayday]

PhilGeis said:

Thanks - Think you should read these carefully - they do not support “synergism” of the combination.

Whoops, I missed the mueller-hinton broth. I think that’s also neutral pH, so the sorbate and benzoate would have no significant disassociation and the results are completely irrelevant to low-pH cosmetic formulas.

My original question still stands though about the why and how for the use ratio for Na-benz and K-sorb.

I checked out the 2nd ed of your book that you linked in another thread but didn’t find specific discussion on concentrations for benzoate/sorbate. Is that sort of question addressed in the 3rd ed of Cosmetic Microbiology: A Practical Approach?

I should add that I have not yet gotten any textbooks on cosmetic chemistry. If these questions are too elementary, feel free to just point me in a good direction and I’ll really appreciate it! (I’m considering Steinberg’s Preservatives for Cosmetics 2nd ed.) Thank you for the help so far

[Mayday]

Also if anybody knows where to get konjac glucomannan as someone who only has access to repackers/online, it’d be appreciated! I’ve found Now Foods Glucomannan (supplement) and Modernist Pantry Konjac Gum, but am hesitant to order them because I am doubtful they are suitable for making clear gels…

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Abdullah said:

They are often combined at 2:1 benzoate: sorbate so this may be a good ratio. 

I have seen that recommended too, something like 0.15% K-sorb and 0.30% Na-benz. But I would really like to know why!

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@PhilGeis I only briefly searched google scholar and read abstracts, skimmed tables and summaries. Here are the two I found FWIW…

• http://scholar.googleusercontent.com/scholar?q=cache:U6-j852OHIJ:scholar.google.com/
• https://www.koreascience.or.kr/article/JAKO198803041928647.page

Isn’t it popularly touted that together they provide “broad spectrum” protection? The Euxyl K712 brochure claims to be effective against E. coli at 0.5% total (after 168h).

I found another paper looking at sodium nitrite, sodium benzoate, and potassium sorbate independently against E. coli and B. cereus, with the pH range of K-sorb being extended by high salinity and Na-benz showing the most significant effect from lower pH. Na-benz also being the most effective at elevated temperatures (25-35C).

• https://pubmed.ncbi.nlm.nih.gov/8466802/

The impression I’m getting is that Na-benz starting from 0.1% can provide adequate protection alone at ph<4.0, even against E.coli. K-sorb does not, and needs to be in salt water to work against bacteria. Is there any benefit to combining them?

(I am now leaning more towards Na-benz+Phenoxyethanol+Ethylhexylglycerin as a preservative starting point, but all I have at the moment is K-sorb, Na-benz, and Phenoxyethanol.)

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Hello, my name is Christian. I’m new to cosmetic formulation, but feel like I’ve already learned a lot just reading and searching the threads on this forum! This place is a gold-mine of information!

My interest in formulation actually got started when I got curious about the ingredients in the water-based lube brands I was using ????. Lube is gosh darn expensive and I wanted to make it myself to save money since it’s mostly water. I also think there’s room for improvement for higher performance and lower irritation. I don’t care much for “natural” BS and prefer minimalism and safe/effective ingredients.

I’m also an artist and hope to combine that with cosmetic and lube formulation to build a business! (I know about FDA 510(k) and it may be a pipe dream but I just really love lube and sex toys so I’m determined to make it work somehow.)

Aside from lube, I want to try out formulating all
sorts of things, especially coconut-oil based emulsions because I love
the way it smells and feels on my skin.

In general I’m fascinated by cosmetic science and the complexity of all this. I don’t have much of a background in chemistry or organic chemistry, but I’ve been making progress in the fundamentals like learning the Bronsted-Lowry and Lewis theories of acids and bases. Hoping to slowly work my way up to organic chemistry.

Thanks for having me here! I’ll try to only ask good questions and contribute where I can.

[Mayday]

I wonder if @LisaLise could help? I’ve been curious about konjac glucomannan since I read her blog posts on it being nearly equivalent to carbomer.

* https://www.lisaliseblog.com/2012/05/konjac-glucomannan-vs-carbomer-whos.html
* https://www.lisaliseblog.com/2012/04/konjac-glucomannan-plant-based-answer.html

Also that it a synergizes with xanthan gum to massively increase viscosity with such small amounts, and I wonder if that combination may avoid the pilling effect while keeping the texture pleasant.

* https://skinchakra.eu/blog/archives/443-What-you-need-to-know-about-natural-gums-part-II-Gum-blending.html

[Mayday]

To hop on this question, is it unsafe to adjust pH using strong acids like HCl? I’ve seen that NaOH (strong base) can be used to adjust pH up for ingredients like Carbomer.

Is there a difference in potential for skin irritation at the same pH?

Are there any general principles to know if an acid or base can be safely used in cosmetics (aside from checking to see if it’s been used successfully by reputable manufacturers)?

CosmeticIngredientReview doesn’t return a search result for Linear Alkyl Benzene Sulphonic Acid, any alkylbenzene, or hydrochloric acid (in my case): https://online.personalcarecouncil.org/jsp/IngredInfoSearchResultPage.jsp