How Salt Thickens Cleansers

Salt is used in more than food. It plays a starring role in cosmetics too. Cleansers such as body wash, shampoo and hand soaps are mixtures of ingredients called surfactants. Surfactants are surface active agents made up of a water loving (hydrophilic) head group and an oil loving (hydrophobic) tail.  The hydrophobic tail is usually made up of Carbon atoms derived from coconut or palm oils. The water loving head groups contain a charge similar to the end of a magnet. Cleansers that can be thickened with salt include anionic surfactants with large head groups.

Anionic Surfactant Molecule:

Types of Surfactants

• Negatively Charged (-) Anionic Surfactants

• Positively Charged (+) Cationic Surfactants

• Neutral (no charge) Nonionic Surfactants

• Both Positively (+) and

  Negatively (-) Charged Amphoteric Surfactants

Micelle (image source: https://commons.wikimedia.org/wiki/File:Micelle_scheme-en.svg)

When added to water, surfactants adsorb to the surface of the water and then start to arrange themselves into spheres called micelles. The tails face in and the head groups face outwards into a spherical shape. As electrolytes (salt) are added, the spherical micelles change into rod shaped micelles which take up more space and pack together as the mixture is stirred. The closer the surfactants get to each other, the thicker the product becomes. This is how some cleansers can be thickened with salt while others need other ingredients such as polymers to thicken.