Preservation and water activity...

I preserve anything I add water to. But I've seen some videos on YouTube from a cosmetic chemist saying that if a formula has 5% or less of water that a preservative is not required because the water activity is low enough to not be a concern. I was a bit confused because I thought that water activity couldn't be accounted for accurately without specialized equipment. If anyone could shed some light on the 5% or less, I'd appreciate any insights. Thank you!


  • I heard In a video , where Perry said that , even if you don't use water in a formulation you should use preservative , coz formulation may be contaminated by a wet finger . 
    Please don't follow Youtubers , follow only qualified Chemists or a qualified person in this field . 
  • You can't decide to skip preservatives based on water activity alone, only microbial challenge testing can determine that.
    You can add some water mist, microbial challenge tests.

  • MicroformulationMicroformulation Member, Professional Chemist
    Water Activity (Aw) must be measured (the equipment is uncommon), it can not be extrapolated. It is not as one-dimensional as simply water percentage in the Formula. Also, like any preservative system (as has previously been stated) it must be proven with testing. Microformulation Cosmetic Consulting provides Custom Formulations for both large Commercial accounts as well as smaller entrepreneurs. We can provide Naturally compliant Formulations under the NSF, NPA, Whole Foods and USDA Organic Certifications. BS.Pharm Albany College of Pharmacy, Union University.
  • Thank you all. What you all said is what makes sense to me. That's why I was confused to see a chemist say 5% or less was a measure to determine this. Appreciate the input.
  • PerryPerry Administrator, Professional Chemist
    @RSullivan - Anyone can call themselves a cosmetic chemist and make a video on Youtube. 

    But even if the person is a cosmetic chemist, it's easy to be misinformed or mistaken. I'm sure there are things I believe that are not exactly correct.

    Someone who misunderstands the importance of preservation and the concept of water activity could easily come the conclusion that formulas with 5% or less water don't need preservatives. But they would be wrong. It would be relatively easy to demonstrate microbial growth in such products.

    I personally believe that omitting preservatives from any formula is a mistake & an unnecessary safety risk. Product safety is more important than a marketing position.
  • aquariustyeaquariustye Member, PCF student
    I was looking at a list of ingredients from a leave-in conditioner spray and the product was marketed as natural.

     I was curious what their preservative was because most of the conditioner sprays are going to be mostly water if it's not for styling. I posted their ingredients.

    The preservatives are Grapefruit Seed Extract, Leucidal Liquid filate, Citric Acid, and Sea Buckthorne  and maybe the essential oil blends (I'm assuming that part of the preservation in the seabuckthorn extract could be preserved with sodium benzoate (0.5%), potassium sorbate (0.2%)) ? Because when I looked at it on Making Cosmetics that's what they used to preserve it at a pH of 3.5-4.5 ) Would the potassium sorbate and sodium benzoate count as part of the blended preservatives they used and is that why seabuckthorne is listed last? Am I wrong for assuming this? Because from what I understand those preservatives would not properly preserve aloe vera with that much water because I see that aloe vera juice is the second ingredient followed by a hydrosol. When I looked at the list of preservatives that Jane Barber put out she said that GSE and Leuconostoc/Radish Root Ferment Filtrate (Leucidal Liquid) was not recommended.  In the case of aloe vera/hydrosol which is very hard to preserve,
    she said "it could be done with as much as 50% aloe vera or hydrosol and pass preservative test just ask supplier for the microtest or batch(or Certificate of Analysis) of aloe/hydrosol you buy - check that to see that it is lower than 100 cfu/gram/ml 
    no staph, Candida albicans or gram negative bacteria''  At what percentages would all the preservative have to be to be effective if the aloe and hydrosol were 50%? Looking at the list of ingredients I could only speculate but the preservative system must be very good if they are selling it. Your thoughts?

    Lavender Water, Aloe Juice, Herbal Infusion of Horsetail, Burdock, Chamomile, Hibiscus, Ginger, Irish Moss & Nettle, Flaxseed Gel, Babassu Oil, Castor Oil, Pro Vitamin B5, Sorbitol, Algae, Kelp, Jamaican Black Castor Oil, Agave Nectar, Natural, Fragrant & Essential Oil Blends, Grapefruit Seed Extract, Leuconostoc/Radish Root Ferment Filtrate, Citric Acid, Sea Buckthorne 
  • The 5% or less of water myth has been around for a while but I am extremely skeptical. Here are just a few of the real world examples of products I have seen contamination with low water/anhydrous formulations. 

    Eye shadow - anhydrous microbiological contamination (we guessed that it was a thumb print contaminating the powder) as a result of a production issue when packed. This was a preserved product but the preservative system was overwhelmed - which lead to another investigation into the manufacturing facility, but that's another story. 

    Humidity causing microbiological contamination in a body powder type product. 

    I sent a cream based product for microbiological testing that had ~3% water in it because I was skeptical it would be safe on the market - it was already contaminated and failed challenge.  

    These are just a few of the examples I have seen over the years that I can remember off the top of my head. 

    Now I'm not saying that you can't create some lovely formulations using low aw as a way to preserve products but this needs to be tested not extrapolated as RSullivan and Perry states.
Sign In or Register to comment.