How To PH Balance Soap & Test The Level

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If you have spent any amount of time on soap making blogs and forums, you will have come across the issue of trying to PH balance soap. It can be a tricky business, but if you have the right tools and knowledge at your disposal you shouldn’t have too much trouble checking the pH of soap. 

In this post, I’m going to outline exactly what ‘PH’ is, why it is important for soap makers, and then finally how to check whether you have managed to actually create soap thats safe. Let’s get started. 

how to use ph strips for testing soap

What Is PH?

Before we come to soap, we should discuss what PH actually means. PH is, most simply, a scale of 0-14 that indicates how acidic or alkaline something is. The lower the number, the more acid and the reverse for further up the scale. 

You may have come across this in your high school chemistry class. If you want to get a bit more technical, you could say that PH is the measure of the concentration of protons in a solution. While it is possible to come across a solution that has a PH that is off this scale, we shouldn’t have to worry about that with ordinary soap making.

Why Do We Need To PH Balance Soap?

When ready, pour the lye solution into your oils

So, we come to the real work. Why is it important to balance the PH of a soap? Well, firstly, it depends on what the soap is intended for. 

If you want to make soap to clean your home, you need not worry too much about how alkaline your soap is. It’s only when soap is intended for the skin do we really have to worry about the PH of it. 

So, when you calculate a soap recipe, using a soap calculator like the one I have here on my blog, your job is to make sure that you don’t end up with a lye heavy soap. 

If your soap is lye heavy, which means there are lots of unsaponified lye left in your soap, it can irritate the skin. This is especially so for anyone with sensitive skin, including young children. 

However, sometimes things go wrong. Soap recipes can be very sensitive if you are not super careful about weighing your ingredients. So checking the PH of your soap is important. Let’s take a look at how you would go about doing this. 

How Do You Check The PH Of A Soap?

Be sure to test your liquid soap to make sure it is PH balanced

You’ve made a gorgeous batch of soap. You have cut it into bars and waited 4 weeks to cure. But how do you know if the PH balance is right? You may wish to give it to a friend with sensitive skin, or your soap is intended for your own children. The last thing you want to do is irritate the skin. 

This is where PH testing comes into the soap making process. There are two reliable ways to test the PH of your soap, and ultimately what kind of soap you’re making will determine which one you’ll use. 

If you’re making a solid bar of soap, I usually always recommend using what is called a universal indicator strip (or ph strip). These can be purchased on Amazon, they are little rectangles of paper that have been treated with a special solution that will change color when it comes into contact with a liquid. 

Depending on how alkaline or how acidic the solution is, the strip will change color. You can then compare the strip to the color-coded key that always comes with your indicator strips. Usually yellow, orange, and red indicate the presence of acid. Green is a perfect balance. Green-blue, blue, and purple indicates the presence of alkali. 

You Won’t See Red When Making Your Soap!

When you’re making soap, it is highly unlikely you will ever see yellow, orange, or red. Due to the nature of lye as an alkali, it just won’t happen. Essentially, you’re looking for your soap to be a PH of between 7-10, although if someone does have sensitive skin, aim for an 8 or 9.

Now, I know what you’re probably thinking, how on earth do I test a solid like soap with a universal indicator strip. Simple! Just suds up your soap a little. Wet a couple of fingers and rub it into the surface of one of your bars of soap. You can use a glove if you are worried about irritation. Then, lay an indicator strip over the damp area and check it against the key. 

If you are making liquid soap, all of this stands true, and the ph strips should work just fine. However, you can get hold of a universal indicator solution, which will work well on both solid and liquid soap, if you prefer. 

How To PH Balance Your Soap

Step 10: Check the PH of your soap with a universal indicator strip, should be between 6-9 but can be lowered with a 1:4 ratio of citric acid and distilled water

PH Balance Of Your Lye Based Liquid Soap

Now, what to do if the PH of your lye-based liquid soap is too high? Simple! Just add some citric acid. You’ll need to dilute it first, though. To do this, combine 1 part citric acid to 4 parts warm distilled water. Add a little to your liquid soaps, stir, wait for 5 minutes and then test again. Repeat until you achieve a PH of between 7-10.

PH Balance Of Your Soap If Using Surfactants

If you are making liquid soap using natural surfactants you will need to check the PH level. This needs to fall slightly onto the acidic side with a range of between 4 and 6. If it’s a little too high, you can use a PH modifier to bring it down. You can use Lactic acid or Citic acid.

If using Lactic acid simply add a couple of drops at a time checking as you go. If using Citric acid, you will need to dilute it in a solution of 10% Citric acid to 90% distilled water. Make sure to add small amounts at a time and then test again, repeating until you reach a reasonable PH. You don’t want to risk wasting your entire batch by adding too much of your PH modifier.

Because this recipe contains a surfactant, it is highly unlikely that your soap will test lower than a 4 on the PH scale, so don’t worry too much about needing to raise it.

Test the PH level of your soap, it should be slightly acidic between 4 and 6.

PH Balance Of Your Hard Cold Process Soap

If you find your solid bars of cold process soap are a bit lye heavy, there’s not a whole you can do about it. This shouldn’t really happen, providing you’ve followed a recipe from a reputable source and you have weighed your ingredients properly. If you have designed your own recipe, check it with a soap calculator to ensure you have calculated the water to lye ratio correctly.

Final Thoughts 

That’s all your really need to know on the topic, especially for a soap maker. If you want to learn more about the science behind soap making, I definitely recommend my post on saponification, as well as my recent post about lye

Soap making is a science, as much as it is an art. While you can make soap without needing to know all of the complicated chemistry behind it, understanding it will make you a better soap maker. This is especially true in this case, as an unbalanced soap can lead to irritation.

If you have any questions about what I’ve discussed today, don’t hesitate to leave a comment. I will do my best to answer any of your questions.

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