The wording Surfactant is derived from wording surface active agents. They are grouped into four main categories: Anionic; Non-ionic; Cationic & Amphoteric. They come in various forms, liquids, granular & fine powders, each performing differently, and used in various ways.
Surfactants are cleansing ingredients, often used in shampoos 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.
How to choose a surfactant.
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 will boast good foaming but can be known to irritate the skin so often an amphoteric (very mild) surfactant is added. Catatonic 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). 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 as their charge is controlled by the pH of the solution it is used in. They become negatively charged when used in an alkaline solutions & they become positively charged when used in an acidic solution. These surfactants are very mild and have good dermatological properties. Amphoteric surfactants produce less foam than anionic surfactants and are not sensitive to water hardness.
Non-ionic surfactants are non-charged and very mild and often used in products aimed at babies. They are therefore compatible with all other surfactant groups. Non-ionic surfactants are not sensitive to water hardness.