"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:
A surfactant does two main things:
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 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:
In my DIY Homemade Shampoos you will find:
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You might also like:
SwiftCraftMonkey (Shampoo Chemistry), About.com (How Shampoo Works), Buffalo (Chemistry of Shampoo), ChemistryViews.org (Shampoo Science)
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By Heather Katsonga-Woodward