Sodium Salts vs Potassium Salts in Soap: What’s the Difference?

When browsing ingredients on soap labels, you may notice terms like sodium olivate, sodium cocoate, or potassium olivate. At first glance, they look complicated — but these are simply the salts of natural oils created during the soap-making process.

Understanding the difference between sodium salts and potassium salts explains why some soaps are solid bars, while others are liquid. And it also reveals a fascinating history, especially in the making of traditional Marseille soap.

• Sodium Salts (e.g. Sodium Olivate, Sodium Cocoate)
  Created when oils (like olive or coconut) are saponified with sodium hydroxide (caustic soda).
   They produce hard, solid soaps with long-lasting bars and a rich, creamy lather.

• Potassium Salts (e.g. Potassium Olivate, Potassium Cocoate)
  Formed when oils are saponified with potassium hydroxide (caustic potash).
   These result in softer or liquid soaps, with a looser texture and more fluid lather.

Both types are true soaps, just with different characteristics.

The distinction between sodium and potassium salts goes back to early soap-making history.

• In regions near the Mediterranean coast, ancient soap-makers had access to soda ash (sodium carbonate) from salt deposits. This gave rise to the tradition of hard, solid soaps — like Savon de Marseille.

• Inland regions, especially in forested areas, relied on wood ash, which contained potash (potassium carbonate). These produced soft or paste-like soaps, more easily dissolved in water.

Thus, the geography of natural resources shaped the development of soap traditions.

• Sodium salts are used when a durable, long-lasting bar soap is desired. Perfect for personal cleansing, laundry, and household soap blocks.

• Potassium salts are preferred for liquid soaps. They dissolve easily in water, making them ideal for pump bottles, black soap pastes (Savon Noir), and multi-purpose liquid cleaners.

Traditional Marseille soap has historically been made with sodium salts of olive oil, producing the iconic 72% olive oil cube soap. This solid bar was prized for laundry, stain removal, and skincare.

But Marseille’s heritage also includes Savon Noir (Black Soap), made with potassium salts of olive oil. This softer soap was traditionally used for cleaning floors, household surfaces, and even as a natural insecticide in the garden.

Together, they represent two sides of Provence’s soap-making expertise:

• Sodium soaps → hard, versatile cubes for laundry and body.

• Potassium soaps → liquid and paste soaps for home and garden cleaning.

Soap Type Made With Texture Uses Example

The difference between sodium and potassium salts explains why some soaps are hard and others are liquid. Both are natural, biodegradable, and eco-friendly, but each has its own role.

• Sodium salts = solid soaps like Marseille cubes.

• Potassium salts = liquid soaps like Savon Noir.

Together, they form the foundation of France’s proud soap-making tradition, offering sustainable and versatile cleaning solutions for body, home, and beyond.