Castor Oil in Soap and Shampoo Bars

Why castor oil?

One Earth Body Care focuses on sustainability in part by using materials sourced as close to home as possible. Some of our ingredients, such as castor oil, are not regionally produced, so we like to discuss why we use them. We use castor oil as a small percentage of our shampoo bars and some of our soaps. This post takes a look at this special oil.

A cluster of twelve brownish red speckled castor seeds, Ricinus communis

Castor seeds, photo by H. Zell (own work)

The castor plant, Ricinus communis L.,

is a shrub native to tropical and subtropical areas and naturalized to warmer temperate regions. Its fatty seeds consist of 30 to 60% oil, which is extracted by cold or hot pressing. Brazil, China and India produce more than 90% of castor oil exports. The castor plant has high annual seed production and grows on marginal soils, and the mealy byproduct of castor oil production can be used as fertilizer1.

Chemical Structure of ricinoleic acid, showing carbons, double bond and hydroxyl groups.

Chemical structure of ricinoleic acid

Castor oil is unusual.

It is dominated by a single fatty acid, ricinoleic acid, which can make up more than 90% of its fatty acid profile, and it contains more ricinoleic acid than any other commercial plant. Ricinoleic acid is unique among plant-based fatty acids in that it is hydroxylated (contains an OH group), and contains a single double bond, on the interior of the carbon chain. When used directly on the skin, castor oil has antiinflammatory and analgesic effects that are attributed to the ricinoleic acid2.

The chemical properties of castor oil

make it valuable in bodycare products. It is viscous and resists oxidation/spoilage. The viscosity is a result of the OH group within the chain, which leads to hydrogen bonding between oil molecules. In soap, castor oil provides great conditioning and improves the quality of lather created by other oils (e.g., coconut) by making the lather thick, creamy and stable. This makes castor oil an important component of shampoo bars.

Now when you lather up with a handmade shampoo or beard bar, you’ll know the thick, creamy lather and soft conditioning are thanks in part to castor oil!

If you found this post interesting, read about other soapmaking materials here!


  • Charles Cladel Posted September 18, 2017 9:32 pm

    Love reading your very thorough and informative articles Anne! AM going to start collecting some that very abundant jewel weed and boil those goodies right out of it and store that liquid for my next encounter with poison ivy. Also am to make that apple cider hair rinse as a supplement to your shampoo bar. Have been compiling a list other of your natural products. Very happy to be using your marvelous wares on a regular basis. What a lot of thought, knowledge, skill and creativity goes into each one. Thank you!

    • annealtor Posted September 20, 2017 3:10 pm

      Thank you for your nice comments!

  • Nancy Posted September 18, 2017 9:16 am

    I like the scientific explanation.

    • annealtor Posted September 20, 2017 3:10 pm

      Thank you, fellow scientist!

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