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Is PEO/PEG incompatible with parabens?
Does PEO/PEG deactivate parabens or tend to pull it out of solution? Preservatives for Cosmetics, 2nd. ed (Steinberg) notes thatParabens are inactivated (partially or fully) by strong hydrogen bonders, such as highly ethoxylated compounds like polysorbates, and compounds like cellulose derivatives, proteins and lecithin.If it’s the ethoxylated portion of a polysorbate that is interfering with the parabens, it stands to reason that PEG may deactivate parabens as well, since they are the same structure. And of similar concern would be any significant amount of PEGylated molecules. This comment here notes that:a word of warning: if you’re using ethoxylated emulsifiers (steareth-21,
oleth-5 etc.) there is a real chance that one or both of your parabens
will crash out of solution and crystalliseContext: Starting with a base preservative broth of:- 0.20% Calcium Disodium EDTA
- 0.20% Methylparaben
- 0.04% Propylparaben
- 0.50% Phenoxyethanol
This formula is crystal clear until I introduce PEG-90M at 0.5% or 1.0% (fairly high, this is for a lubricant). The sample becomes slightly hazy.I’m thinking I will try further dropping the propylparaben from the solubility limit at 25C (maybe to 0.32%) , but I am wondering if these ingredients are known to be generally incompatible from a preservative system standpoint. -
7 Replies
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Recommend propyl parabens at 0.1%. Is your level 0.04% or 0.4 (lower to “0.32”)?
Why would you want Ca NaEDTA? If intent is to sequester divalent cations - why waste capacity?
Test it. -
@PhilGeis thank you for your response!The sources I have access to list Propylparaben solubility in 25C water as 0.05% (Preservatives for Cosmetics 2nd ed) and 0.04% (a brochure I found). I have perhaps seen it discussed here that paraben solubility may be increased by pre-dissolving it in a surfactant (?) but that is not very applicable to my formulas.I started with 2000:1000ppm methyl:propyl from your advice on other posts, but was unable to keep the Propylparaben from precipitating when cooled to 25C. I haven’t found a good source for the sodium salts as a residential homecrafter.Ca NaEDTA is because the CIR Final Report Safety Assessment for EDTA (PRS285.pdf) notes that calcium chelators are toxic to urothelium. My understanding is that the membrane weakening effect of calcium chelation is helpful for boosting preservative efficacy, but so long as the final formula passes PCT I would prefer to make that trade-off.
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I am actually doubtful now if the slight haze is due to the parabens. Substituting parabens for Sodium Benzoate produced the same effect. I think it is the specific PEG-90M I am using.What I am more concerned about is if there’s a likely potential for full deactivation (a la polysorbate) between PEG and methyl/propylparaben.
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If you’re concerned with loss of efficacy - test with and without.
Why do you bother with EDTA if you’re compromising the objective of its addition?
Further - toxicity of your concern exists but is not highlighted in CIR’s summary of EDTA in-use safety for cosmetics*. Think it arose from use of the material directly to urinary tract for stones. What is your risk assessment - NOEL and how would exposure from your product exceed it?*”Based on the available data, the Cosmetic Ingredient
Review Expert Panel found that these ingredients* are safe as used
in cosmetic formulations.”these ingredients include sodium and calcium sodium salts of EDTA
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@PhilGeis My mistake, the paper was referenced by the CIR review only passingly. “Rationale for local toxicity of calcium chelators” (Urol Res (1992) 20:19-21, W. Oosterlinck).Oosterlinck 1992 studied the effects of citrate and various EDTA salt solutions (additionally with/without TEA) on inducing bladder lesions in rats.From Oosterlinck 1992, any amount of calcium chelation (including 100mM citrate + TEA) is potentially damaging/irritating to urothelium. The average female urethra is only 3-4cm long with the proximal 2/3 being urothelium—not enough buffer distance from the meatus to make urinary ingress of a lubricant impossible.The CIR describes EDTA-metal-ion chelates as forming in the order:
- Na+ < Ca2+ < Fe2+ < Co2+ < Zn2+ < Cu2+ < Pb2+ < Fe3+
Calcium Disodium EDTA is used intravenously to treat heavy-metal poisoning (including Pb2+). While I’m not well-informed on the specific chemistry of EDTA chelation, my understanding is that Calcium Disodium EDTA can still complex with the other metal ions starting with Fe2+ in solution.Re: preservative testing. I will be sure to test preservative efficacy and substitute with a more appropriate system as needed. -
@Mayday The studies mentioned in the CIR for EDTA salts are for their physiological use. That’s completely different to their use in cosmetics, so you don’t need to worry about that.
Now, using calcium sodium EDTA might reduce its chelating capacity compared to disodium or tetrasodium EDTA. Sodium can be replaced easily in the sodium EDTA salt, so spots for chelation are available, but calcium is not that easy to be replaced since it forms more stable complexes with EDTA.
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As ketchito said - you wasting chelating capacity to no benefit.
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