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“Take it with a grin of salt.”
Compared to all the high-tech ingredients stealing the cosmetic spotlight, salt might seem a comparatively drab commodity item, but it has played a key role in the story of mankind, as has been expertly depicted in Mark Kurlansky’s Salt: A World History1. Salt funded the Erie Canal and the Great Wall of China. Gandhi’s salt march of 1930 led to independence for India. Salt has also given sauerkraut and olives to the global gastronomy. Salt is not only an essential cosmetic ingredient, but one that is still undergoing technical refinements and novel applications.
The Chemistry of Salt
In elementary chemistry, when acids and bases react, they form a salt and water. This is called a neutralization reaction:
HA + BOH —> BA + H2O.
By far the most common salt is sodium chloride, NaCl, but many other salts find use in personal care. Many raw materials contain significant quantities of salt. Commercial cocamidopropyl betaine is 35% solids, but only 30% surfactant. The difference between solids and actives is 5% NaCl. Disodium cocamphodiacetate is 40% surfactant, 10% NaCl. Many surfactants, such as ammonium lauryl sulfate, come in different viscosity grades, with salt content being one key variable.