Are preservatives obsolete?

I've been making liquid dishwashing soap for a couple of months now. I was wondering why is there a need for a preservative? As far as I know, soap molecules disrupt the lipid membrane of most microorganisms such as bacteria and thus disabling it. So if soaps like dishwashing liquid can do this, why is there a need for biocide/preservatives (like methylparaben or Isothiazolinone) in the first place?
Thank you so much in advance.


  • PerryPerry Administrator, Professional Chemist
    I think they said it best in Jurassic Park.  "Life, Uh, Finds a Way"
  • PattsiPattsi Member
    if it's for personal use u can do whatever u want, if it's gone bad u can just toss it out. but if u sell it and can manage to get 2-3 years shelf life with out preservatives then congratulation and could you please share ur how to.
  • Awesome reference you got there sir @Perry . I guess I'll now be adding preservatives. I hope tardigrades won't be living in my soap anytime soon.  
    Thank you sir @Perry
  • I'll give you an update @Pattsi if my preservative-free dishwashing liquid formulation becomes resilient to any microorganisms (I highly doubt that it would last for years, but if it does, I'll share my formulation). Cheers mate!
  • mikethairmikethair Member
    edited July 17
    If you are making true soap (liquid and solid) by saponifying plant oils, then preservatives are not required. ISO 29621 "Cosmetics — Microbiology — Guidelines for the risk assessment and identification of microbiologically low-risk products" covers this.

    We produce these types of soaps in our GMP Certified production facility. As part of our GMP standards for 10+ years, we have performed Challenge Tests on these soap products, and they are always negative. When we export to the EU, they recognize that microbial data is not required for these products.
    Dr. Mike Thair
    Cofounder & Chief Formulator
    Indochine Natural
  • Thank you sir @mikethair. I am making liquid soap based from SLES and LABS. I guess I'll be adding preservative now
  • chemicalmattchemicalmatt Member, Professional Chemist
    With low Aw and high pH you may get away with it, and saponification products ala Dr. Mike's usually meet those parameters, but I don't advise it. A little Kathon never hurt anybody, and I mean anybody.
  • PerryPerry Administrator, Professional Chemist
    @chemicalmatt - you must not have done a Google search on Methylisothiazolinone reactions. For some, saying Kathon is safe is fightin' words.

  • zeteinzetein Member
    Today I learn: they can eat your surfactant !

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