A surfactant is a surface-active ingredient; in products they break the surface tension between water and oils so that they come together easier. Surfactants are mainly used in shampoos and bodywashes as a functional ingredient. They solubilise dirt by lowering the surface tension of water, (making the molecules slipperier, becoming less likely to stick to themselves and more likely to cling to dirt) which is then washed off and removed from the hair. They can also be used as an additional ingredient for lotions by utilising their unique properties.
How To Choose A Surfactant
There are four main categories: Anionic; Non-ionic; Cationic & Amphoteric. Often more than one surfactant is used in a formulation, as they all have different properties. Depending on what properties you are trying to achieve your requirements will vary.
For example, an anionic surfactant is often used as the ‘primary’ surfactant as they are very cleansing, and have good foaming capabilities, however, they can be known to irritate the skin. To lessen the irritation to skin additional ‘secondary/multifunctional’ surfactants are selected. An amphoteric (very mild) surfactant can be added to an anionic surfactant, and cationic surfactants are added when a conditioning element is desired.
Anionic surfactants are negatively charged and not compatible with cationic surfactants. They are effective foam boosters and strong cleaners (some can irritate skin). They can be sensitive to water hardness. Anionic surfactants are often combined with secondary non-ionic and amphoteric surfactants to minimise the impact of using a strong anionic surfactant.
Cationic surfactants are positively charged and not compatible with anionic surfactants. They are commonly used in hair care products due to their conditioning & anti-static properties.
Amphoteric surfactants can be positively charged or negatively charged; this is because their charge is controlled by the pH of the solution it is used in. They become negatively charged when used in an alkaline solution & they become positively charged when used in an acidic solution. These surfactants are very mild and have good dermatological and detergency properties. Amphoteric surfactants produce less foam than anionic surfactants, they have good compatibility with anionic surfactants and are not sensitive to water hardness.
Non-ionic surfactants are non-charged and very mild, often being used in products aimed at babies. They are therefore compatible with all other surfactant groups. Often not suitable as standalone surfactants, they blend well with an ionic and amphoteric surfactant. Non-ionic surfactants act more as an emulsifier or thickening and conditioning surfactant. Non-ionic surfactants are not sensitive to water hardness.