What Are Surfactants And Why Does A Shampoo Need Them?

"Surfactant" is essentially a fancy word for detergent; it is short for "surface active agent". Surfactants are used very widely in cosmetic and household cleaning products. Basically, anything used for washing, for example:

• Body and face wash
• Hand wash
• Bubble bath
• Liquid soap
• Washing liquids and powders for clothes and dishes
• Shampoo
  

A surfactant does two main things:

• It’s a cleansing agent: it reduces the surface tension of water thereby allowing the water to wet things more thoroughly.
• It’s an emulsifying agent: it binds water and fats, oil or grease into an emulsion allowing them to be washed off.

Greases, oils and fats are insoluble in water on its own. A surfactant has a hydrophilic (water-loving) head and lipophilic (oil-loving) or said differently, hydrophobic (water-hating or water-repelling) tail. This means one side of the surfactant attracts water whilst the other side attracts oil and in so doing the two bind together.

Water on its own would fail to wash off greases and would thus be ineffective for washing oils and greases in hair. A wide range of surfactants are commercially available.

In addition to cleaning, you might want a shampoo to have other qualities so you add surfactants or other ingredients such as:

Foam boosters: increase the capacity of a product to produce foam, e.g. glycerin.

Hydrotropes: enhance the water solubility of another surfactant.

Solubilizing agents: help other ingredients dissolve in water when they would not otherwise do so.

Thickeners: help your formulation thicken.

Film formers: moisturizing and conditioning ingredients that make hair feel soft, e.g. hydrolyzed proteins (oat, wheat, etc.), crothix, glycol distearate, water soluble oils, fatty alcohols (e.g. cetyl alcohol) and silicones.

Fragrance: makes your hair smell great.

Slip-enhancers or silicones: to help detangle or keep hair tangle-free.

Shine boosters: to make hair look shinier and healthier.

Scalp soothers: to sooth an itchy scalp.

• There was a time when my scalp used to itch like crazy and for those few months, before I discovered that I was probably allergic to something in my water filter, I enhanced all DIY and bought products with peppermint essential oil.
• I live in a hard water area so I was trying to soften the water a little for the sake of my hair and in the process created an alternate, worse problem!

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There is little point in adding certain humectants e.g. sodium lactate to shampoo because they just wash off without giving any benefit. I prefer to save those for my conditioners. Glycerin is a good humectant to add, however, because in addition to being a humectant it is a foam-booster and it helps to condition and moisturize the scalp.

Other properties to look out for in a surfactant:

• How strong is it? If you have dry hair you want a "mild" or "very mild" surfactant. Whereas those with oily hair may find them “too moisturizing” – something that doesn’t exist in the world of my hair!
• How well does it work at different pH levels?
• How well does it work in hard vs. soft water?
  

In my DIY Homemade Shampoos you will find: 

• Sodium Cocoyl Isethionate (SCI) - a very mild anionic surfactant
  
• Decyl Glucoside - a very mild non-ionic surfactant
  
• Cocamidopropyl Betaine - a mild amphoteric surfactant
  
• Coco Glucoside - a mild non-ionic surfactant
  
• Lauryl Glucoside - a mild non-ionic surfactant

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You might also like:

• Neno Natural's Free DIY Shampoo Recipes

Ref:
SwiftCraftMonkey (Shampoo Chemistry), About.com (How Shampoo Works), Buffalo (Chemistry of Shampoo), ChemistryViews.org (Shampoo Science)

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