If you’ve ever wanted to make your own homemade liquid castile soap, this step-by-step guide will show you exactly how. Castile soap, originally from the Castile region of Spain, is a natural product made with only olive oil, making it an excellent choice for those with sensitive skin. Unlike bar soap, liquid castile soap is versatile—it can be used as a body wash, dish soap, or even a purpose cleaner. Plus, making your own ensures that you control the ingredients, avoiding harsh chemicals found in store-bought soaps.

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Why Make Your Own Liquid Castile Soap?

Gentle on Skin: Made with pure olive oil soap, this recipe is ideal for those with dry skin.
No Harsh Chemicals: Unlike commercial soaps that contain sodium hydroxide or artificial additives, this soap is a biodegradable soap that’s safe for personal use.
Versatile: It works as a homemade liquid hand soap, body soap, dish soap, or even laundry detergent.
Cost-Effective: Making your own soap recipes can save money in the long run, and you can create different essential oils blends for unique scents.

Ingredients and Equipment for Homemade Liquid Castile Soap

Ingredients

565 grams organic olive oil or extra virgin olive oil
140 grams potassium hydroxide
450 grams distilled water
5+ cups of additional distilled water for dilution
Essential oil blend (optional, for fragrance)

Equipment

A large crock pot or slow cooker
Measuring cup
Immersion blender (also called a stick blender)
Non-plastic mixing bowl for the lye solution
Spatula for stirring
Protective gear: gloves, goggles, and a mask
A well-ventilated area for working with lye

Important Safety Warning About Lye

Lye, whether it’s sodium hydroxide or potassium hydroxide, is a very strong chemical that can be dangerous if not handled properly. When mixed with water, it heats up quickly and can cause serious burns if it touches your skin or eyes.

Always wear gloves, goggles, and a mask when working with lye, and make sure you’re in a well-ventilated area to avoid breathing in the fumes. Never pour water into lye—always add lye flakes to water slowly to prevent splashing or overheating.

Keep children and pets away while making soap, and have vinegar nearby to help neutralize spills. If lye gets on your skin, rinse with lots of cool water right away. If irritation continues, seek medical help. Being careful with lye is important for staying safe while making soap.

Step-by-Step Homemade Liquid Castile Soap Instructions

Prepare Your Work Area

Since you will be working with potassium hydroxide, which causes a strong chemical reaction when mixed with water, safety should be your top priority. Choose a well-ventilated area, such as near an open window or outside, to avoid inhaling fumes.

Put on protective gear, including gloves, goggles, and a mask.
Use only heat-resistant, non-reactive materials like stainless steel, glass, or heavy-duty plastic for mixing.
Keep vinegar nearby to neutralize any lye spills.
Cover your workspace with newspaper or parchment paper to protect surfaces from spills.
Make sure pets and children are kept away during the process.

Heat the Olive Oil

Pour 565 grams of olive oil into a crock pot or slow cooker and turn it to high heat. Olive oil is the only oil used in this recipe, making it a true castile soap. Allow the oil to warm up before proceeding. This ensures that when the lye solution is added, the reaction occurs at a steady and controlled rate.

Mix the Lye Solution

This is one of the most important and potentially dangerous steps in the process, so follow these directions carefully.

Measure 450 grams of distilled water in a non-plastic, heat-resistant container.
Slowly add 140 grams of potassium hydroxide flakes into the water. Never pour water into the lye; always add lye flakes to the water to prevent dangerous splattering or overheating.
Stir gently until the flakes dissolve completely. The mixture will heat up quickly and produce fumes, so stand back and avoid inhaling them.
Let the lye mixture cool slightly while the olive oil continues to heat in the crock pot.

Combine the Oils and Lye Solution

Carefully pour the lye solution into the heated olive oil in the crock pot.
Immediately use an immersion blender (also called a stick blender) to begin mixing.
Blend in short bursts, pausing every 30 seconds to avoid overheating the motor.
Continue blending until the mixture reaches a thick, pudding-like consistency. This stage is called “trace,” and it indicates that the oils and lye have fully combined.

Cook the Soap Paste

Now the slow cooking process begins. This step ensures that all the lye is converted, making the soap safe for use.

Allow the thickened mixture to sit for 5 to 10 minutes, then blend again briefly.
Continue this process until the mixture becomes too thick to blend.
Once it is too thick to mix with an immersion blender, place the lid on the crock pot and let the soap paste cook on high for four hours.
Stir the soap paste with a spatula every hour to help it cook evenly. It will gradually turn more translucent as it saponifies.

Diluting the Soap Paste

After four hours of cooking, your soap will look like a thick, gel-like paste. Now it’s time to turn it into liquid soap.

Add five cups of distilled water to the crock pot.
Break the soap paste into smaller pieces using a spatula to help it dissolve.
Reduce the heat to low, cover the crock pot, and let it cook for another eight to ten hours.
Stir occasionally to encourage the soap paste to dissolve evenly.

Adjusting the Consistency

After the cooking time, the soap will still be thick and may have some clumps. To get it to the right liquid consistency:

Add small amounts of distilled water, one cup at a time, stirring well after each addition.
Allow the mixture to cook for 30 minutes to an hour after each addition before adding more water.

Cooling and Storing Your Soap

Once the soap has reached the desired consistency, turn off the heat and let it cool. If you want to add fragrance oil or an essential oil blend, do so now. Tea tree and lavender are popular choices for scent and antibacterial properties.

Pour the cooled soap into bottles or a soap dispenser for easy use. I love using half gallon mason jars.
Store in a cool, dry place.
If the soap thickens too much over time, you can add warm water to thin it out.

Cost Comparison: Homemade vs. Store-Bought Castile Soap

Making your own liquid castile soap is not only a rewarding DIY project but also a cost-effective alternative to store-bought versions. Based on current ingredient prices, a gallon of homemade liquid castile soap costs approximately $14.46 to make. This includes the cost of distilled water at $1.37 per gallon, olive oil at around $0.50 per ounce, and potassium hydroxide lye at $12.50 per pound.

In comparison, well-known brands can cost over $60 per gallon, making the homemade version a much more affordable option. Not only do you save money, but you also have complete control over the ingredients, ensuring a high-quality, natural soap without unnecessary additives.

Uses for Your Homemade Liquid Castile Soap

As an easy hand soap recipe for the bathroom or kitchen
As a homemade hand soap with added essential oils
As a DIY body wash for sensitive skin
As a biodegradable soap for cleaning purposes

Conclusion

Making your own liquid castile soap is a good idea for anyone looking to switch to a natural, customizable, and cost-effective alternative to commercial soaps. With this simple liquid castile soap recipe, you can create a high-quality soap that’s perfect for personal use, cleaning, and gifting. Experiment with different essential oils, adjust the consistency with a water discount, and enjoy the benefits of true castile soap made from pure olive oil.