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What is Castile Soap?

Mary McMahon
Updated May 17, 2024
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Castile soap is a soap made with fat of purely vegetable origin, rather than animal fats such as tallow. This type of soap has historically been highly prized and viewed as a high quality soap which is gentle on the skin and useful for a range of other applications. Many stores sell castile soap, and this soap is a specialty of several regions in Europe, where it is made with various traditional ingredients. It is also possible to purchase this type of soap base for the purpose of blending your own soaps.

This soap is said to be named for the Kingdom of Castile, a region in what is now known as Spain. Evidence seems to suggest this soap actually originated in Northern Italy, and spread outwards from there, although this soap is so ancient that it is a bit difficult to pin down the precise details of its history. In Castile, the soap was made with olive oil only, and some people differentiate between capitalized Castile soap, made with olive oil, and lower case castile soap, made with other vegetable oils.

Although olive oil is the traditional base oil, the soap can be made with coconut, hemp, avocado, almond, walnut, and many other vegetable oils. The composition of the soap will vary slightly, depending on which base oil is used. In pure form, the soap is white, hard, and odorless. Many soapmakers also make a liquid version, which is odorless and pale cream to white, often thickening in cool weather.

Once the base is made, castile soap can be scented with various floral ingredients, blended with oatmeal and other coarse materials to assist with exfoliation, or treated in other ways to create soap with specific purposes. The soap is often used as a hand soap in fine hotels, and the soap can also be used as a general body soap, a shampoo, or a general cleaner. These soaps can be used to wash clothes, scrub floors, bathe pets, and in a variety of other situations when something needs to be cleaned.

This type of soap is often highly prized because it is made with natural ingredients, appealing to people who want to be environmentally conscious. It is also very gentle, suitable for people with sensitive skin along with delicate surfaces and fabrics ranging from soft stone to silk. Some people like to blend their own soap, using a base and essential oils.

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Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a About Mechanics researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments
By anon1005731 — On Nov 04, 2021

Very informative pointers on the why and what of castile soaps and the benefits of castile soaps. Great read.

By anon945940 — On Apr 15, 2014

@anon335876= I agree with you. A 'real' Castile soap is made with 100 percent olive oil. If others are used but olive is still the main, it is called a Bastille.

This business of castile (not capitalized) being soap made of any vegetable origin oil is a tad annoying. The word is morphing too far from its true meaning.

By anon359090 — On Dec 15, 2013

All soaps are made with lye. It is what causes the fats (oils) to react and congeal and the product is soap!

After the first 24 hours, most curing is complete, although the longer the soap is cured, the harder and more mild it becomes. It is made with olive oil and no other types of oil.

If somewhere on internet it says "make lye free soap," it's usually what us dispatchers call rebatching. They take, for instance, Ivory soap, grate it and add a little water, microwave it and flip it in molds. I hope this clarifies it for you all.

As for lye being a carcinogen, than the whole modern world and the past culture would have cancer. On a medical note, because I'm in the medical field, when I'm not making soap, we all make abnormal cells daily. If our body doesn't kill off the abnormal cells, it can become cancerous.

By anon335876 — On May 24, 2013

Castile soap refers to the soap created in the region of Castilla in Spain. The soap is made with only extra virgin olive oil. If other oils are added, it is not considered Castile soap. There are a handful of manufacturers of this soap that use a very secret process to make this fabulous soap. And there is only one manufacturer in the USA that learned the process in Spain. If the pseudo castile soap contains coconut oil, palm oil, hemp, or any other, is not a true castile soap. It's just a plain vegetable soap.

By anon321752 — On Feb 24, 2013

I have used liquid castile soap and will not go back to regular liquid soaps. My favorite is Bohemian Apothecarium, but Dr. Bronner's is pretty good too (not as thick as Bohemian). I want to start making my own bar soap, so thank you for sharing this.

By John57 — On Nov 18, 2012

I have very sensitive skin and castile soap is one thing I have never had any problems with. I like to make my own and add essential oils for just the right scent. My favorite is when I add lavender oil to the soap. Not only does the soap leave you feeling clean, but the scent of lavender is both refreshing and relaxing.

By Mykol — On Nov 18, 2012
@julies -- I have been able to find the castile bar soap at my regular grocer, but if you are looking for anything other than that, you probably have to go somewhere else. If you can't find it locally, you can probably find it online.

I have a small bottle of liquid castile soap that I use for a lot of things. This is like an all purpose soap that you can use all over the house. I use it to give my dog a bath and to clean the floors with, in addition to bathing myself with and washing my hair.

I love using something so gentle and safe for the environment. Castile soap has been around a long time and I hope it starts making a comeback. If someone isn't used to using castile soap, they are always surprised at how well it lathers and soft it leaves their hands.

I keep this in my guest bathroom and the bathroom off the kitchen, and get comments from guests about it all the time.

By julies — On Nov 17, 2012

I like the way castile soap cleans, but if I am using it to wash my face with or in the shower, I like something that has some scent to it. I recently bought a peppermint scented castile soap that I absolutely love.

The peppermint isn't too strong, but strong enough that it energizes me in the morning. I buy my castile soap at the health food store, but would love it if I could find it at my local grocery store.

By SarahSon — On Nov 16, 2012

@anon126777 -- It is nice how soft and smooth your skin feels after using castile soap. Other soaps leave your skin feeling very dry. If you are looking for something natural to remove your eye makeup with, I use olive oil. This works just as well as expensive eye makeup removers I have bought and is very moisturizing for the area around your eyes as well.

By anon295591 — On Oct 07, 2012

Thank you for sharing this. I have used a castile soap in the past (Bohemian Apothecarium) which I loved. I always wondered exactly what Castile soap was actually. It's interesting to know the history behind the soap.

By anon141138 — On Jan 09, 2011

@comment#7 - Do some research before you start spouting inanities.

All soaps are made with lye -- every one. If there's no lye in the process, it's not soap, it's detergent. Lye is a strong alkali, but not a carcinogen.

Finished, properly cured soap does not contain any lye; the chemical reaction (saponification) splits the sodium ion (Na) from the hydroxide ion (OH), as it likewise splits the lipid chains from the glycerol in the oils/fats used.

Folks, please - don't believe everything you read! On the internet, anyone can say anything they want (even me). Do your own research, then if you can't determine credibility, maybe go with the most common answer!

By anon137193 — On Dec 26, 2010

Lye is a carcinogen, so if you are trying to find a healthy, safe soap, castile soap is not one.

By anon137105 — On Dec 26, 2010

I've been using Kirks Castile Soaps for years and I love them all. I use the shampoo, the liquid hand soap, and the bar in the shower. After a while, i couldn't find the soaps in the stores so I had to send away for them from the Kirks company.

By anon126777 — On Nov 13, 2010

just tried it for the first time tonight. bought three bars at the grocery store- very inexpensive- washed my face with it when I came home from work. Made my skin feel great! very smooth. But it didn't take off my eye make-up. Guess that's good. means there are no chemicals?

By anon113822 — On Sep 26, 2010

Kirk's Castile bar soap is great.I found it while searching for an alternative to standard chemical filled soap bars. It lathers better than any soap I've ever used, but it doesn't last as long as standard chemical filled soap bars. Meaning, I have to get a new bar out a little more often than regular bar soap, so it's a good thing it lathers so well. -ega278

By galen84basc — On Sep 17, 2010

How can I make castile liquid soap? Is that easer to make than the solid version?

By zenmaster — On Sep 17, 2010

It's actually not too terribly difficult to make homemade castile soap and shampoo.

There are a million variations, but the basic castile soap ingredients are lye, olive oil, and water, so that's not too hard for anybody to find.

There are a ton of recipes online, so I'm not going to outline it here, but the thing to remember is that all your materials have to be non-reactive.

That means you need a stainless steel or enamel pot, and a glass jar to mix the lye -- don't even bother using anything else, you'll just ruin your jars and pans.

By pleats — On Sep 17, 2010

I got turned on to castile soap when I lived in Greece for a while, when I started using olive oil soap on a regular basis. When I came back to the states I started using Dr. Bronner's Castile Soap which seems to work about the same.

I've also heard of Kirk's Unscented Castile Soap, but I've never tried it -- can anybody tell me if that's any good?

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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