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Castile Soap 101: Properties of a Castile soap

May 22, 2013

If we've met before and you've bought one of our soaps, one of the things I may have told you about it is that true Castile soaps (that is, only those made purely from olive oil) have earned themselves the nickname 'the newborn soap'. This is because soaps made purely of olive oil are arguably the mildest soaps you can find.

Now, Castile soaps have another nickname: Queen of Soap. I believe it got the name because when Castile soaps were first made in the 1500s, they were used exclusively by royalty and noblemen. Now that olive oil is somewhat more ubiquitous, I like to think that it's kept the nickname because Castiles require some TLC, but more on that in another post. 

Soapmaking resource website Cole Brothers gives a description of the properties of different oils when they are made into soap. Here is what they say about olive oil:

Olive oil is excellent as a base oil in soaps, either in whole (Castile soap) or in part...olive oil prevents the loss of your skin's natural moisture, softens skin and attracts external moisture to your skin. It helps keep your skin soft, supple and younger looking. 

From DailyGlow.com:

Soap made from olive oil is naturally hypoallergenic, which means that it has little likelihood of causing an allergic reaction. Olive oil is very similar to your natural skin oils, so your skin responds well to olive oil. The soap helps to add moisture to your skin and can help you to cleanse your skin without stripping the natural oils.

Another soapmaking resource site, Summer Bee Meadow, has this to say: 

Olive oil attracts external moisture to your skin, helping to keep skin soft and supple.

It also cites olive oil's high oleic and linoleic acid content, which contributes to a soap's mildness and skin conditioning benefits. Compare the following oils popularly used in soapmaking, and their respective attributes:


Oil Lauric Acid Linoleic Acid Myristic Acid Oleic Acid Palmitic Acid Stearic Acid
Olive   5-15%   63-81% 7-14% 3-5%
Coconut 39-54% 1-2% 15-23% 4-11% 6-11% 1-4%
Palm   9-11% 1% 38-40% 43-45% 4-5%


Lauric and myristic acid contributes to a soap's hardness, cleansing properties, and fluffy lather. Lauric acid also can be drying to the skin.

Linoleic acid is responsible for the conditioning, silky feel of the soap.

Oleic acid is conditioning, gives a slippery feel to the soap, inhibits lather, and is mild to the skin.

Palmitic acid makes a hard bar, contributes to a soap's cleansing properties, and makes a stable lather (not quite as easy to wash off as fluffy lather).

Stearic acid also contributes to the hardness of the bar and stable lather.

So what exactly does all this mean?

Put simply, it means that a true Castile soap makes a fairly hard bar that doesn't lather much (and yes, is kinda slimy due to its high oleic content), but is very mild and gently cleanses and moisturizes your skin!

My next post will be about how soap works and why lather isn't all it's fluffed up to be! (Oooohh, controversy!)



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