When making handmade soap, soapmakers often experiment with different additives to enhance the quality and performance of their bars. One ingredient that frequently comes up in discussions is citric acid. While some claim that citric acid lowers the pH of soap, this is not true for lye-based soap. Instead, citric acid plays a much more practical roll. It acts as a chelator, helping soap perform better in hard water.
It’s important to note that citric acid can lower the pH of soaps made from synthetic detergents. Such as Sodium Cocoyl Isethionate (SCI) or Decyl Glucoside. This is not the case for traditional lye soap. In handmade soap, citric acid reacts with lye, forming sodium citrate, which does not affect the soap’s final pH.
If you’ve ever noticed a filmy residue on your sink or shower after using soap, or if your soap struggles to lather properly in certain areas, the culprit is likely hard water. Fortunately, citric acid can help resolve this issue. Let’s take a closer look at what citric acid does in soap, how to use it properly, and what adjustments you need to make to your formula to ensure a successful batch.
Understanding Hard Water and Its Effect on Soap
To appreciate why citric acid is beneficial in soap, it’s important to understand how hard water affects soap’s performance. Hard water contains high concentrations of dissolved minerals, primarily calcium and magnesium. These minerals can significantly impact how soap functions.
When soap is used in hard water, it reacts with the calcium and magnesium ions to form insoluble compound. Commonly known as soap scum. This reaction reduces the soap’s ability to cleanse and lather effectively, leading to:
- A filmy or sticky residue left on skin and surfaces
- Soap that doesn’t rinse off completely, potentially causing dryness or irritation
- Reduced lather, making it harder to create a rich, foamy wash
- Bars that dissolve faster due to increased soap scum buildup
To counteract these effects, soapmakers use chelating agents. Which bind to the calcium and magnesium ions before they can interfere with the soap. This is where citric acid comes in.
How Citric Acid Works in Soap
When adding citric acid to a handmade soap recipe, it reacts with sodium hydroxide (lye) to form sodium citrate. A natural chelating agent. Sodium citrate binds with the minerals in hard water, preventing them from reacting with the soap. This results in:
🛁 Reduced soap scum, keeping skin, hair, and surfaces cleaner.
🌊 Improved lather, allowing the soap to work more effectively even in hard water.
🧼 A longer-lasting bar, since less soap is wasted reacting with minerals.
🚿 Better rinsing, helping to prevent residue buildup on skin and surfaces.
Unlike EDTA (a synthetic chelator commonly used in commercial soaps), sodium citrate is a natural alternative that enhances soap’s performance without harsh chemicals.
Why Citric Acid Doesn’t Lower the pH of Handmade Lye Soap
One of the biggest myths about citric acid in soapmaking is that it lowers the soap’s pH, making it milder or more skin-friendly. This idea likely comes from its behavior in other cleansing products.
For synthetic detergent-based cleansers, such as those made with Sodium Cocoyl Isethionate (SCI) or Decyl Glucoside, citric acid can indeed lower the pH because those surfactants are not reliant on saponification. However, in traditional lye soap, citric acid does not function the same way.
In cold-process and hot-process soapmaking, all citric acid reacts with lye to form sodium citrate, meaning there’s no free citric acid left in the final bar. Since pH is determined by the presence of acidic or alkaline components, and sodium citrate is neutral, the overall pH of the soap remains unaffected.
If you want to lower your soap’s pH, you would need to use other techniques, such as superfatting (leaving unreacted oils in the soap) or adding ingredients like yogurt or apple cider vinegar after the saponification process. However, citric acid alone will not achieve this effect in lye soap.
How to Properly Use Citric Acid in Soap
While citric acid offers significant benefits, it does require some adjustments to your soap recipe. This is because citric acid reacts with lye, consuming some of the sodium hydroxide that would normally be used to saponify the oils. If you don’t compensate for this reaction, your soap may end up with excess unsaponified oils, making it softer or more prone to early rancidity.
How Much Extra Lye to Use with Citric Acid
To ensure proper saponification, you must adjust your lye calculation when using citric acid. The general rule is:
🧪 For every 1% of citric acid (based on oil weight), add an extra 0.624% sodium hydroxide (lye).
Example Calculation:
Let’s say you are making a 1,000g oil batch and want to add 2% citric acid:
- Calculate citric acid amount: 2% of 1,000g = 20g citric acid
- Calculate extra lye needed: 20g × 0.624 = 12.48g extra lye
- Add this extra lye to your total lye calculation to ensure proper saponification
This adjustment ensures that there is enough lye to fully react with both the citric acid and the oils in the soap.
How to Add Citric Acid to Your Soap Recipe
Adding citric acid to your soap is easy, but it’s important to incorporate it correctly to avoid issues like graininess or incomplete reactions.
1️⃣ Dissolve the citric acid in your lye water first. This allows it to fully react with the sodium hydroxide, forming sodium citrate before it encounters the oils. Adding citric acid directly to the oils can result in a gritty texture in the final soap.
2️⃣ Make sure to adjust your lye calculation as described earlier to compensate for the lye consumed by the citric acid.
3️⃣ Continue your soapmaking process as usual. Once the sodium citrate is formed, it becomes a stable part of the soap and works throughout its lifespan to improve performance in hard water.
Final Thoughts: Is Citric Acid Worth Using in Soap?
Absolutely! While it may require a little extra calculation, the benefits of using citric acid in soapmaking far outweigh the effort. By forming sodium citrate, citric acid:
🛁 Prevents soap scum and residue buildup
🌊 Enhances lather even in hard water
🧼 Extends the life of your soap bars
🚿 Improves rinse-off for a cleaner feel
🍃 Acts as a natural alternative to synthetic chelators
Just remember that citric acid does not lower the pH of lye soap—that’s a myth. While it may reduce the pH in detergent-based cleansers, in handmade soap, it functions solely as a chelating agent. With the right formulation, you can create bars that work beautifully in all water types.
Do you use citric acid in your soap recipes? Have you noticed an improvement in your soap’s performance? Let us know in the comments!
