Preservative for pH 9-10 liquid soap

What are my options for an alkaline based hand soap solution preservative?
Does a liquid hand Castille soap mixed with oils and glycerin need a preservative? 
Many thanks in advance for any help/advice given!


  • @Leo Usually bar soaps from saponification of either tallow or vegetable oils, are the ones that are basic (alkaline). If you have a liquid soap, you could actually have it at a pH closer to the skin (roughly around 4.5-5.5). If you want to stay at that pH range, isothiazolinones are very effective, same as formaldehyde-releasers (like DMDM hydantoin, Diazolidinyl urea, etc.), but that is if you're ok with that type of preservatives. 

    I do believe your liquid Castille soap needs since you need quite some watter to haved in a liquid form. 
  • LeoLeo Member
    Will the acidification with for instance citric acid as a preservative affect the foam?
    Are there any other preservatives that are "more natural" that can function at pH 9?
  • If you lower the pH you will loose the bubbles. 
  • Here is an ingredient list. No preservative but an antioxidant. Look at the advisory information.😱

    INGREDIENTS (INCI): Aqua, Potassium Cocoate (Saponified Coconut Oil*‡), Potassium Palm Kernelate (Saponified Palm Kernel Oil*‡), Potassium Olivate (Saponified Olive Oil*‡), Glycerin*, Potassium Hempseedate (Saponified Hemp Oil*), Simmondsia Chinensis (Jojoba seed oil*), Citric Acid, Tocopherol (Vitamin E), Helianthus Annuus Seed Oil (Sunflower Oil) *Certified Organic Ingredients/ ‡Certified Fair Trade Ingredients

    Advisory information:

    Vegetarians and Vegans. Don’t drink soap. If cap clogs, poke it clear, do not squeeze the bottle. Soap can clog and spurt with pump dispensers. Keep out of eyes. Flush eyes well with water for 15 minutes. Consult a physician if irritation persists.

  • If the liquid soap has a pH 9 - 10, a preservative is unnecessary. Refer to ISO
    29621 "Cosmetics — Microbiology — Guidelines for the risk assessment and identification of microbiologically low-risk products."

    We have a GMP Certified production facility producing a lot of liquid soap, and export globally. These products are Notified with cosmetics authorities and all the necessary testing is done in our in-house labs and verified by external labs.

    Dr. Mike Thair
    Cofounder & Chief Formulator
    Indochine Natural
  • ketchitoketchito Member
    edited September 12
    @Leo  If you have a liquid soap, you'd need to go very low on pH to prevent microbial growth, and as @Dr_Sara mentioned, it'll impair foam and detergency, and it'd also increase the chance of instability (for instance, CAPB behaves as a cationic at low pH, which will interact with anionic surfactants forming a precipitate). It can be done, but you should be very careful with the ingredient selection...also, you'll need a very good GMP system in place to guatantee that your water for instance is of very high quality, since low pH helps prevent microbial growth, but it won't avoid your product being contamined from external sources.
  • LeoLeo Member
    If the pH of the soap is around 9, do I need a preservative?
    I see that a lot of these products have citric acid which affects foaming and performance?
  • @Leo Citric acid in a liquid soap at a pH above 9 will be present as its salt (Citrate) rather than the acid form.

    Regarding the need for a preservative, if your idea is not to include one, there are a couple of readings you might want to take a look at:,

    So, pH as a sole strategy could be tricky, since being at least at a pH of 10 for shrinking the risk of microbial growth (I've seen products being contaminated at pH around 9), can also mean that you might have free alkalinity in your product. Of course this is more sensitive for leave on products, but for individuals with reactive skin (not to mention if the product reaches your eyes) and under repetitive use, that might cause some problems.  
  • for true soap- a pH of 9 is good. I would add a preservative. 

  • LeoLeo Member
    What preservative would work at pH near 9? 



    Please let me know.
  • LeoLeo Member
    glycerol monolaurate or monolaurin or propanediol or caprylhydroxamic acid to name a few. Any experience with these or other preservatives for pH near 9?
  • Hi @Leo I have used phenoxyethanol in liquid soap.
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