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  • Cosmetic Microbiologist Here. I Can Help Answer Your Germ Questions

    Posted by The_Microbiologist on December 31, 2013 at 10:03 am

    Hi Everybody,

    My name is Ben Tanner and I am the microbiologist in charge of Cosmetic Test Labs in Texas.  My lab specializes in cosmetic microbiology, such as preservative challenge tests and aerobic plate counts. 

    I was on the old forum for some time as “CosmeticTestLabs.”  Anyway, I think there is a great group of people on this forum and so I like to share my microbiological expertise when I can.  Feel free to ask me any germ/preservation/contamination/infection/test questions you might have.  I usually check in every few days.

    Happy formulating and testing!

    - Ben

    Loretta replied 10 months, 4 weeks ago 20 Members · 53 Replies
  • 53 Replies
  • Microformulation

    December 31, 2013 at 10:04 am

    Welcome Back Ben! By the way I have sent some clients your way (can’t say which due to NDA) and each one has had a positive experience.

  • MakingSkincare

    December 31, 2013 at 11:44 am

    Hi Ben

    Welcome back to the forum.  Thanks for offering to help - I would love to have your views on some points made in this article - 

    http://www.americanpharmaceuticalreview.com/Featured-Articles/38885-Antimicrobial-Preservatives-Part-Two-Choosing-a-Preservative/ specifically…..

    Benzyl alcohol and phenoxyethanol should not be formulated with non-ionic surfactants eg polysorbate 80. They will interact and such interactions may not involve conventional chemical transformation, but concern more subtle phenomena e.g. hydrogen bonding and complex formation. Thus the overall level of preservative in the product may not change, but unless the preservative is available in the “free” form its efficacy may be compromised.

    The article also states:-

    EDTA can interact with benzoic acid ….and..

    Adsorption onto excipients, especially those with large surface areas or on to container / closure systems can also remove preservative(s) from solution for example
    - benzoic acid by kaolin
    - phenoxyethanol by pvc plastic, cellulose based excipients
    - sorbic acid/sorbates by plastics (polyproylene, PVC and polyethylene)

    The antimicrobial efficacy of phenoxyethanol is reduced in the presence of the cellulosic suspending agents such as HPMC.

    I’m wondering what your experiences are with the above and whether you agree with points raised in the article?
  • vitalys

    January 1, 2014 at 4:39 am

    Welcome back, Ben :)

  • Chemist77

    January 1, 2014 at 5:32 am

    @MakingSkincare I have read the link you have posted, I would like to ask if a non-ionic emulsion too renders the preservative ineffective e.g. my emulsion has fatty alcohols, glyceryl stearate and some ester oils. I am not using PS 80.

  • The_Microbiologist

    January 1, 2014 at 1:03 pm

    Wow, what a nice welcome back to the forum!  Thanks everybody, and thanks Mark for the referrals.  We have sent some folks your way, too.  Hopefully they have found you well.

    MakingSkinCare - That article is a gem.  I looked over it briefly and will read it in full later.  In the meantime, I can confirm that polysorbate 80 does neutralize certain classes of preservatives.  In fact, we use it in our all-purpose neutralizing broth for that very purpose in the lab.  Here is the product insert and formula if you are interested.  In that document (and in lots of scientific literature), it says the purpose of polysorbate 80 is to neutralize substituted phenolics.  I don’t think phenoxyethanol is technically a substituted phenolic (it would seem to me to be more like a monophenyl ether), but it is structurally similar to many substituted phenolics so the two chemicals probably should not be present in the same cosmetic product if the goal is to make it microbiologically stable.

    I am not as familiar with adsorption of preservatives onto plastics, though I know some long-time formulators who consider the plastic type of their packaging to be effectively one more formulation variable.

    As for the cellulosics, I would anticipate some interference with preservative effectiveness, but in a minor way.  We see this with almost all thickening agents.  Maybe the best example comes from a contact lens solution maker several years ago.  I don’t have all the information, but I think that basically what happened in that instance is they added a thickening agent to their lens solution to aid in eye feel that bound up some portion of their preservative, thereby knocking out some efficacy and allowing some pathogenic fungi to gain a foothold. 

    Most antimicrobial agents carry a positive charge - and this is just a broad theory of mine - which physically leads them to the negatively charged cell wall, where the rest of the molecule does the destruction.  Since cellulose is a huge molecule with lots of charge variation over its surface, it would not surprise me to see it bind up some preservatives. However I would not expect them to be too tightly bound so the effect may not be a formula-killer.

    milliachemist - some non-ionic surfactants do interfere with antimicrobial efficacy but usually in a minor way and the effect can be expected to vary depending on other aspects of the formulation such as pH.  I don’t have a list in my head of which ones should be avoided, but I have definitely seen instances where removal, substitution, or scale-down of a non-ionic surfactant improves antimicrobial activity.

  • Chemist77

    January 1, 2014 at 2:03 pm

    Great one Ben, thanks once agsin for a perfect 10.

  • MakingSkincare

    January 2, 2014 at 5:58 am
    Thanks so much Ben.  

    Preservation is such a complex and fascinating area (I’m confessing to being a bit of preservative nerd!).  I’ve written reviews on commonly used preservatives and am always looking for more info.  I’ve got a few more questions - I’ll just concentrate on the key ones here and if it’s OK I will message you a couple of other questions, since I don’t want to hog your post.

    Does polysorbate 60 also neutralize substituted phenolics?  A lot of people in my group use ewax which contains it.

    The questions below, are obviously formula dependent…

    what would be your overall opinion of naticide or leucidal liquid (incl the SF version)? I have been cautious not to recommend them as I have not seen independent studies on their effectiveness. 

    Thanks again Ben for your kind help. 
  • Anonymous

    January 2, 2014 at 8:44 am

    Hi Ben,

    I actually just received a bid from Cosmetic Test Labs to do my testings I need done for my products! So I may be working with you guys real soon. :-) 
    Anyway I have a question about what preservative would be the best fit for “natural” product lines. I know, I prefer not to use “natural” because it means nothing, but it’s the best way to sum it up…from the earth, plant-based, not synthetic, no parabens.
    Would a combo of Grapefruit Seed Extract, Citric Acid and Vitamin E be sufficient for a formula that is about 90% water based ingredients (aloe juice, Lime Hydrosol) and 10% oils? A couple of the other ingredients also say they have “mild preservatives” properties to them. If this wouldn’t be enough to ensure my products are safe, what do you recommend to fit the needs/wants of my product line?
    Thank you so much in advance for your knowledge in this area. It is much appreciated. :-)
  • The_Microbiologist

    January 3, 2014 at 11:15 am

    Hi MakingSkinCare and Tasiashton,

    Perhaps I can kill two birds with one stone with this statement about “natural” preservatives (including Leucidal):

    Can a cosmetic formulation be microbiologically stabilized using one or more “natural” preservatives like Leucidal, sorbic acid, and lactic acid?  Yes.  Is it easy?  No!  Is it cheap?  No!  Will it always work with “tough” formulations? No!

    And about grapefruit seed extract and vitamin E, I have never been wowed by them.  That’s not to say they don’t work, just that I don’t recall ever seeing it happen, and I vaguely recall some scandal where grapefruit seed extract appeared to have been spiked with quaternary ammonium compounds.

    We get a lot of samples through the lab for preservative challenge testing, many from customers we haven’t worked with before who are submitting formulations to us that are as new to them as they are to us.  When they use traditional preservatives (even retailer-preferable traditional preservatives like phenoxyethanol), their success rate on challenge tests is very high.  I estimate they fail only one in every 5 or 10 tests.  That’s great, because challenge tests take a long time to conduct and are relatively spendy. 

    On the other hand, when they use natural preservatives it often takes a few rounds of testing and reformulation for them to pass.  That’s good for the lab but bad for them, and my heart goes out to them when I see them give up altogether rather than throw in a tiny amount of synthetic preservative and go to market :(  

    So have I seen Leucidal work, yes.  Do I think it is as efficacious as most of the traditional preservatives, no.  But on the other hand, many traditional preservatives are being unfairly vilified.  So unfair or not, there’s a great big and trendy marketing trade-off to be considered.

    Frequently we see customers use antifungal preservatives such as sorbic acid in combination with Leucidal.  That seems to be a pretty good place to start and I’m sure the folks at Active Micro Technologies (makers of Luecidal) could give some other suggestions, too.

    MakingSkinCare:  As for polysorbate 60, I doubt it interferes but am not certain.  As for the proposed formulation 1% GC/D GMCY and p-Anisic/Dermostoft, I just don’t know.  I am pretty sure that your formulation expertise - even as related to preservation - exceeds mine!  I am a “test it and let’s see” sort of guy, which I suppose is a good fit for a testing lab owner :)

    Tasiaashton:  Thanks for giving us a shot!

    Thanks all for the great discussions.

  • Microformulation

    January 3, 2014 at 12:57 pm

    Ben, Great post! My opinion on Natural preservatives is right in line with yours.

    Robert Zonis was posting regarding Leucidal before the site crashed. Through him and several other sources I heard rumblings regarding issues with Leucidal in the last quarter of 2013. Primarily the issues were with Yeast/mold coverage so Potassium sorbate is the way to address that.

    Grapeseed Extract is an over hyped “preservative.” I will not open that can of worms, but I would not recommend it to anyone.

  • Bobzchemist

    January 3, 2014 at 1:49 pm

    We are currently testing Leucidal. At this point, I can’t give any credence at all to unfounded rumblings and/or rumors.

    All I’ll say about GSE is that opinions differ.
    I will also point out that we’ve found it to be extremely helpful to use a chelating agent whenever we use a “natural” preservative system.
  • MakingSkincare

    January 4, 2014 at 8:02 am
    Ben, thanks so much for your response.

    Re leucidal, that was my conclusion too - in the absence of independent studies confirming that it’s broad spectrum, I don’t recommended it on my preservative review page.  Ditto with the GSE.  Bobzchemist - would be great to see what your testing reveals.

    Great point about adding a chelator Bobzchemist.  Reducing the amount of “bug food”, unbound water and adding auxiliary ingredients such as glycols also helps.
  • isaiah

    January 5, 2014 at 3:04 am

    tell me the tests done of a finished product in the micro lab

  • Microformulation

    January 5, 2014 at 1:02 pm


    Chelating agents are able to enhance
    the efficacy of most preservatives. This occurs as the chelator removes
    metal ions from cell walls of the microbes. The weakened walls then
    allow the biocide to penetrate and destroy the microorganisms. Although
    the boosting effect of chelating agents on preservatives is well known,
    the environmental fate of these materials has been debated. To avoid the
    environmental discussion about chelating agents, readily biodegradable
    alternatives have been introduced to the market.

    I use a chelator with PE9010 each time to boost its efficacy. This need was passed onto me several years ago by Wolfgang Siegert at Schulke. It can be challenging as EDTA is a big no no in most “Natural” standards (NPA, NSG, WF’s). In that case I will generally use Dermofeel PA-3 from Dr. Straetmans (Kinetik in the US).

  • Chemist77

    January 6, 2014 at 6:17 am

    @Mark In our old threads I read somewhere that apart from the ‘natural standards’ issue there was this efficacy issue as well. IIRC (learnt it from Duncan to concise everything) tetrasodium salt has to be used above pH 7 and disodium salt below pH 7. Could you please correct me if i am wrong??? Secondly, are there similar issue with sodium phytate too?????

  • The_Microbiologist

    January 6, 2014 at 10:17 am


    The only micro tests typically done on finished product are aerobic plate counts for bacteria and fungi.  Those tests tell a person how many bacteria and how many fungi are present in a given gram or milliliter of product, which in turn indicates whether or not the finished product meets a company’s specifications for acceptable quality for release/sale.  Less than 100 bacteria or fungi per gram or milliliter is a common specification, though less than 10 bacteria or fungi per milliliter or gram is more typical for eye-area cosmetics.

  • Anonymous

    January 10, 2014 at 11:21 pm

    Thanks for the insight and information, Ben! I have already had great interaction with your lab. Andrew has been great to work with and also gave me great advice. And thanks for everyone’s feedback on GSE. I appreciate the help. :-)

  • Polymergirl

    February 1, 2014 at 12:39 pm

    Can you comment on the advisability of many “crunchy” homemakers who make their own liquid soap using regular soap (which they carve into flakes) and water?  It seems to me to be a potentially microbial mess, since they do not add preservative to the mixture.  Do you have anything specific I could tell them to warn them away from this practice? (I offered caution and recommended refrigeration of the product and to discard after one week).

  • Bobzchemist

    February 1, 2014 at 5:52 pm

    Getting the pH up to 12 would make those liquid soaps pretty much self-preserving.

  • The_Microbiologist

    February 3, 2014 at 12:28 pm


    I haven’t heard of that practice before…probably means I spend too much time in the lab :)

    Anyhow, I am sure it’s fine for the day or two.  Then after that I’m pretty sure it would turn into germ soup unless as Bob says the pH is very high. 

  • MakingSkincare

    February 3, 2014 at 4:43 pm
    Ben - “germ soup” - love the phrase!    
    Polymergirl - there are a confusing number of preservatives available - you might find it helpful to look at this review of 27 of them http://makingskincare.com/preservatives/  which details what the preservatives protect against, pH restrictions, compatibilities, %, what phase to add etc.  

    If you need any more help, feel free to PM me.
  • Polymergirl

    February 5, 2014 at 4:57 pm

    Yes, germ soup, that sounds like what they are making. 

  • labtechnician

    February 12, 2014 at 8:38 pm


    We have just a small skin care company and started to formulate natural skin care products. At the moment, we have formulated a moisturizing cream using natural ingredients such as coconut oil, avocado oil, cucumber extracts, vitamin E, etc. We used natural preservatives Parfum (Naticide) 0.8% and Potassium Sorbate 0.7%. Formulation is very good and cream is also very good. We sent for the Preservative Efficacy test and got the following result.
  • labtechnician

    February 12, 2014 at 8:49 pm

    Time Point      S.aureurs            P.aeruginosa         C.albicans      A.brasiliensis

                            CFU/g               CFU/g                    CFU/g                CFU/g

    Inoculum         7.0 x 105              6.7 x 105                  6.9 x 105                1.7 x 105

    0 hour             6.8 x 105             6.1 x 105                  6.1 x 105                1.9 x 105

    7 days                < 10                   < 10                        [NA]                      [NA]

    14 days                 < 10                   < 10                    1.0 x 105                   150

    28 days                 < 10                   < 10                        < 10                       < 10                                   


    What is your opinion regarding this result? How I could reduce the
    survival of yest (C.albicans)? Your help will be really appreciated.


  • The_Microbiologist

    February 13, 2014 at 10:28 am

    Hello labtechnician,

    I notice the “n/a” for Candida and Aspergillus at day 7.  I presume those organisms were just not analyzed at that timepoint.  Is that correct?  Was this by chance an ISO method? 

    Nevertheless this appears to be a well-preserved formula in general.  I see the same “odd” data that you do with regard to Candida.  It’s strange for that organism to have what we would call a “shoulder” die-off curve, meaning slight reduction followed by precipitous reduction.  Usually Candida reduction is much more linear, meaning you’ll loose a log (90%) or so each week on the way down to a final result of non-detection.  It’s possible that the 14 day data was artificially increased by chance, by clumps of organism within the test material or something else.

    If USP <51> criteria were applied it would “pass” so you are in good shape.  If you want to be extra diligent, you could re-test just the Candida and see if next time you see a more linear (sort of more predictable and thus more dependable) die-off.  If you wanted to be even more diligent, you could do that at a different lab.  If two labs get the same result, it’s almost certainly “real.”

    Here is my last note, please verify with your lab that they did separate controls to verify neutralization and recovery from the test sample.  Ask them for the data for that, too.  They should have it and it should be quantitative.  If they don’t, then they’re not doing the test right and it calls into question much of the data.  Feel free to email me privately if that comes up and I’ll help you work through it and re-interpret the data.

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