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What is the difference between soap surfactants?

Mo wants to know…I’m confused. Since I read that surfactant-based liquid cleansers are better than soap, I have been on the look out for a good body wash preferably fragrance free. But now I discover that Dove Bar / Vanicream Bar etc. are not soap but Syndets. What does that mean? There are also Syndet base Liquid face & body washes. What do I pick up?

Right Brain comes clean: It’s easy to understand why people get confused by terms like soap, surfactant and syndet. Personal care marketing companies often hijack words from science and repackage them as friendly marketing messages. Unfortunately, everyone’s marketing message is different so words lose their focused definitions. That’s what has happened with these words. We’ll try to clear it up – busting beauty myths like this is what we do best!

Surfactant Cleaners

Almost all cleansing products are based on surfactants. These molecules have a special construction which makes them compatible with both oils and water. Since oil and water do not usually mix, you need surfactants to remove oils from skin and hair. Soaps and syndets are all surfactants. Detergent is just a synonym for surfactant.

Syndet Made Simple

Syndet is a portmanteau word created by combining the words “synthetic” and “detergent”. It was made up by the beauty industry to make products based on synthetic detergents sound sciencey and special. Synthetic detergent sounds nasty, dangerous and icky. Syndet sounds high tech, fun and friendly.

A common type of Syndet like Sodium Lauryl Sulfate is made by reacting a fatty alcohols with acid.

Fatty Alcohol + Acid = Syndet

Straight Dope on Soap

Soaps were the first surfactants people used for cleaning. They are made by reacting fatty acids with a base (e.g. sodium hydroxide), a process called saponification.

Fatty Acid + Base = Soap

Three things make Soap different from Syndets.

1. Starting material. The starting material for soap is either animal fat (tallow) or natural oils. Syndets start with fatty alcohols which can be distilled from petroleum or derived from natural oils. Sodium Lauryl Sulfate can be made from both Coconut Oil or petroleum distillates. A by-product of soap making is glycerin, a natural moisturizer. Syndets must be formulated with glycerin or other moisturizing ingredients.

2. Reactions with metal ions. The primary problem with soap is that it reacts with metal ions to form a material that is insoluble (can’t be dissolved) in water. This is what causes the “soap scum” you see lining people’s bathtubs and sinks. Syndets do not react like this so it is not a problem.

3. Formulating flexibility. From a formulation standpoint, syndets are much more flexible than soaps. Soaps are generally solids at room temperature and are limited in the number of ingredients you can incorporate in them. Syndets are liquids that can be thickened and made solid.

Syndet Bar

An example of a Syndet bar would be this La Roche-Posay Syndet bar.

It uses standard surfactants like Disodium Cocoamphodiacetate, Coco-Betaine, Peg-7 Glyceryl Cocoate, Sodium Laureth Sulfate, etc.

Beauty Brains Bottom Line

As far as what you should get, that is up to you. If fragrance free is an issue, you could try the La Roche product. You could also try the Dove Bar or other syndet bar. The key to these things is to try different products until you find something you like. Everyone’s skin and preferences are different. Personal experimentation is your best option.

See this page for an experiment demonstrating the difference between soap and detergent.

Do you want to learn more about which beauty myths are true and which ones are bogus?

Download our FREE guide “How To Save Money On Beauty Products.”

{ 4 comments… add one }

  • Mary Ellen Ottman February 12, 2014, 10:30 pm

    I saw your book, “It’s OK to Have Lead in Your Lipstick” on Amazon and bought the Kindle version. It’s highly informative and I recommend it to anyone who wants to know the truth about cosmetics. Thanks for doing such a great job

    • Randy Schueller February 13, 2014, 7:41 am

      Mary Ellen – thanks so much for the kind words!! If it’s not too much trouble could you please post your review on Amazon for us? Perry and I would really your support. Thanks!

  • bernadine hunter August 18, 2014, 8:54 am

    I’m still a bit confused. I use an organic liquid castille soap that is surfacant free, contains no Sodium Laureth Sulfate. It contains:

    Water
    Potassium Oleate (Derived from Organic Sunflower Oil)
    Potassium Cocoate (Derived from Organic Coconut OIl)
    Glycerin (Organic)
    Potassium Citrate
    Potassium Palm Kernelate (Derived from Palm Kernal Oil)
    Palm Kernal Acid (Derived from Palm Oil)

    Would this be considered a soap?

    • Randy Schueller August 18, 2014, 2:21 pm

      Yep, this is a soap. It consists of saponified fatty acids (which come from the oils mentioned in the product.) (Also remember that soap IS a surfactant.)

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