Why do you need multiple preservatives in your cosmetic formula

We received this question here at Chemists Corner central and thought it would be a good one to write an article about.

“Why do the raw material suppliers recommend the combination of presevatives versus using them alone…..for ex: why do the manufacturers recommend a combination of sodium benzoate and potassium sorbate rather than using them individually….

Why you put preservatives in cosmetics

With all the bad press about chemicals used to preserve cosmetics you might wonder why companies don’t just stop using preservatives.  Well, the reason is that cosmetics that contain preservatives are safer than ones that don’t contain preservatives.  This is because disease-causing microorganisms can multiply at exponential rates in cosmetics if there are no chemicals in there to stop them.

And if the consumer is putting a dollop of microbe laden skin lotion on their body, they are bound to contract a disease.  It is just not smart to use unpreserved cosmetics.

The other reason to include preservatives is that when microbes grow in your cosmetic product they can produce foul smelling odors and strange colors.  Consumers just aesthetically do not want to use bacterial contaminated products.  It’s a bit like the same reason people don’t want to eat moldy bread.

What do preservatives do

Cosmetic formulas have all the key factors needed for microbial growth including water, nutrients, and energy.  At a suitable pH and temperature, it will be like a microbial cocktail party.  Preservatives stop growth by killing cells and spores (usually by disrupting cell membranes) or by making the system hostile to growth.  See this article for more about cosmetic preservatives.

Why you need multiple preservatives

So that brings us to the question that started it all, why use multiple cosmetic preservatives?  Basically it’s because some single preservatives do not kill a big enough range of microorganisms.  As a cosmetic formulator you need to ensure that your preservative system will kill any bacterial, mold, or fungi that the formula might encounter.  Since you don’t know what will be encountered you have to plan for every possibility (or at least as many as you can).

There are some preservatives that are able to kill a wide range of microbes (e.g. Alcohol, Parabens, Formaldehyde donors).  That is why these ingredients are so popular with formulators.  Other ingredients like Sodium Benzoate or Potassium Sorbate are only effective against certain types of microbes.  They are more active against yeasts and molds but have a lower activity against bacteria.    One way to compensate for the ineffectiveness of one compound is to include another compound that has the ability to kill other organisms.  By combining preservatives, you increase the spectrum of microbes that your formula can withstand.

Of course, if you used parabens and formaldehyde donors you could be more confident in the effectiveness of your preservative system.  However, for marketing reasons these compounds must be avoided.  It makes your job as a cosmetic formulator a bit harder.

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