Soaps, Syndets and Surfactants
Sumerian clay tablets from 2500 BC found between the Tigris and Euphrates rivers document the early use of soap. Today synthetic detergents known as syndets (i) are increasingly used for gentle cleansing of the skin.
Schematic diagram of surfactants (i)
1 Hydrophilic part
2 Lipophilic (hydrophobic) part
Soaps, syndets and surfactants
Soap is produced even today by a chemical reaction of natural fats (i) with alkali lyes. However, use of soap has the following disadvantages especially for sensitive skin:
- Calcium soap formation and accompanying loss of surfactant properties when used with hard water. Calcium salts deposited on the skin interfere with oil replenishment, leading to rough skin.
- Alkalizing effect: Alkaline hydroxyl ions formed by the hydrolysis of soaps in aqueous solution can irritate and cause alkali eczema, especially in diseased skin.
The development of syndets (i)
These disadvantages led scientists to search for new substances to use for body cleansing. As a result of this work, the end of the 1950s saw the dawning of the era of synthetic detergents, the syndets (i). They have distinct advantages over alkali soaps:
- No alkalizing effect because the pH (i) can be adjusted to the acidic physiological pH (i) of 5.5
- Therefore also suitable for skin with a reduced base neutralizing capacity
- No formation of insoluble calcium soaps
- Little swelling of the horny layer
Solid and liquid syndets (i) have since found a permanent place in skin cleansing – especially for diseased skin.
Surfactants as detergents
Surfactants are molecules that are comprised of a very water-soluble (hydrophilic) part, the head, and a fat-soluble (lipophilic), long-chained segment. Surfactants accumulate preferably at interfaces with the hydrophilic part oriented towards the water phase and the lipophilic part towards the oil phase (e.g. lipophilic dirt).
The importance of surfactant components
Individual surfactants (i) have specific properties, such as the ability to create foam (anionic surfactants (i)) or leave behind a pleasant sensation on the skin (amphoteric surfactants (i)). Therefore, most cleansing products contain a mixture of surfactants (i).