Surfactants in soap: what are they and what they do
- 08/22/2024
The substances behind the soap’s foam and cleansing power
Besides common ingredients, formulations of soaps and other cosmetic products can contain surfactants, like Alchimia Soap’s liquid soaps. But what exactly are surfactants, and why do we find them in soaps? Let’s discover it together.
How surfactants work
From a chemical point of view, surfactants are organic compounds conventionally made up of a hydrophilic part—the polar head—and a hydrophobic part—the non-polar tail. The former has an affinity with water, while the latter is lipophilic, i.e., has an affinity with oily, fatty, or organic substances. Based on this dichotomy, surfactants exhibit different behaviours depending on the solution they are in. For example, they can dissolve in water or wet, oily surfaces. Surfactants modify the surface tension of a liquid.
The surface tension of a liquid is the tensile force tensile force between surface molecules, which contributes to the liquid’s cohesion and affects its interaction with other surfaces. For example, thanks to the water’s surface tension, mosquitos land on water, or a small coin can float instead of sinking.
Surfactants can reduce the cohesion between a fluid’s molecules, allowing substances that normally cannot mix to combine. This results in emulsifying, foaming, or cleansing effects, depending on the case.
How surfactants act in soaps and why they are used
As already mentioned, their action can differ depending on the type of surfactants (anionic, non-ionic, amphoteric and cationic):
- surfactants with a cleansing action: The surface tension of greasy dirt, which naturally prevents it from binding to water, is lowered, making the grease soluble in water and can be removed from a surface. That’s what happens every time we wash our hands with soap or use a cleanser on the body;
- surfactants with a foaming action: in this case, surfactants produce an emulsion between two liquids or the air and a liquid, lowering the surface tension. In the former case (liquid-liquid, e.g., water and oil), the resulting action is emulsifying. When the emulsion involves air, it produces foam upon contact with water. This foam lowers the surface tension of grease, allowing it to be removed. The more foam a soap produces, the greater the presence of surfactants (or their power).
That’s why surfactants are often used in the formulations of liquid soaps and body cleansers. These substances allow the ingredients to bind together and exert their specific action once in contact with water and the skin. Alchimia Soap has always focused on the quality of its products and ingredients, using exclusively plant-based surfactants that are gentle on the skin instead of industrial ones.
