Why and How to Check the pH of Soap & How to Neutralize Liquid Soap When Needed

Should you be checking the pH of your soap? Why could it be important and how do you do it? And how and why should you neutralize your liquid soap if needed?

Checking the pH of your liquid soap: The Why…

Unlike bar soap recipes that tend to use excess oils to chemically react with all of the lye, leaving you extra conditioning oils for your skin, liquid soaps are usually calculated to use either the exact amount of oil for the lye or even use a “lye excess” instead.

Why would you not add extra oils to liquid soap?

Liquid soap recipes are calculated without excess oils to keep the final soaps clear. Having too many oils in a liquid soap will turn the soap cloudy at first, and can even lead to separation if there are enough of them.

Some people like making “liquid soaps” by dissolving bar soap in water, but every time I’ve tried it, I’ve just ended up with a gloppy mess that looks gross in a glass soap dispenser. The soap mixture always separates into two layers, one being opaque and cloudy, and it just doesn’t look very nice. I don’t find it to be as effective as a real liquid soap either.

I personally think that if you want a liquid soap, you should just go ahead and make real liquid soap instead because you’ll have a much nicer final product. It can be intimidating, but once you get over the fear factor, I think you’ll find that it is a rewarding hobby. If you’re interested, I have a recipe up for a liquid castile soap using only olive oil, and a liquid coconut oil soap. (I also developed a couple of takes on a Dr. Bronner’s Liquid Castile Soap copycat recipe. )

I decided to risk a bit of cloudiness in my recipes and worked them to use an exact amount of lye for the oils used so that if people didn’t want to bother with “neutralizing” their soap, they wouldn’t have to.

What does it mean to neutralize liquid soap, and why would you want to?

Because liquid soaps are often made with excess lye, the final soap can have leftover, unreacted lye which can be irritating to the skin. Soaps with unreacted lye will normally have a very high pH due to the alkaline/basic nature of the lye.

If you plan to use the liquid soap for cleaning around the house, having an excessively alkaline soap isn’t really a problem. In fact, it may even be working to your advantage to a certain point. Highly alkaline and highly acidic products can be great cleansers. (Think vinegar and baking soda, or more extremely HCl or NaOH based drain cleaners.) Obviously, if it were too highly alkaline, you’d have to worry about it not eating away at delicate surfaces.

If, on the other hand, you want to use your homemade liquid soap for cleaning your face and body, any unreacted lye and extra alkalinity could lead to skin irritation. In the recipes I posted, I haven’t found it to be a problem for me. I purposely calculated my soaps so they don’t have a lye excess. That said, by calculating the recipe to be “exact,” we are playing in a zone where the final outcome of the soap can be easily swayed by a number of factors. Perhaps the scale you use isn’t very precise or maybe my KOH has more or less water in it than yours and that affects how our soaps turn out. Even the same person using the same recipe with the same equipment could end up with different outcomes each time. (Even temperature can be a factor.) You may end up with a cloudy soap, or you may end up with a slightly harsh one.

That’s why a lot of people feel it is important to test the pH of your soap.

How to test the pH of soap

There are several ways to test the pH of your soap. Unfortunately, there is a lot of confusion about it because it is very difficult to get an accurate pH reading of soap at home, outside of a laboratory.

Inexpensive pH test strips

In the interest of seeing how alkaline my final soap pastes were, I bought pH test strips to test the pH of the soaps. pH strips are great because they’re very inexpensive and easy to use. Because pH measures the concentration of hydrogen atoms in an aqueous (water-based) solution, you will need to dilute the soap paste in distilled water to be able to test it with strips. Even when diluting the soap with distilled water, though, testing with test strips isn’t necessarily very effective. If you don’t add enough soap to your water, or you add too much soap to the water, you may get inaccurate results. (And I haven’t really found a set concentration that you should use for testing either.)

When I first wrote this post, I showed the picture above. It showed that my coconut oil-based liquid soaps tested to be around a pH of 8 and the olive oil-based liquid soap tested to be around 9-10.

A neutral pH is 7, and anything higher than that is more on the alkaline/basic side, while anything with a lower number falls more on the acidic side. Most soaps tend to fall in the pH range of 9-10.

Even at that time, I wrote this…

Let’s take a closer look. I seriously doubt that the coconut oil soap is really at a pH of 8 because at a pH of 8 it would most likely be very cloudy already. I’m guessing it is higher than that, but since I’ve already been using both soaps without any problems, I’m not too concerned about finding the exact pH of these particular soaps.

In the end, I did re-test months later, and on my second attempt, I found it to read around 9 (just like the other soap). My thoughts on that? I feel that it was much more likely user error on my part when testing the first time around rather than the pH increasing with time. I probably had used too little soap paste in the water at the time of testing.

Testing pH with Phenolphthalein

Phenolphthalein is another indicator of pH that is often used by soapmakers, but that I haven’t personally tried yet. It’s a liquid that changes color depending on the pH of whatever you are testing.

pH Meters

More accurate testing can be done with electronic pH meters. You can find inexpensive electronic meters like this one, or more accurate probe pH meters that can test the pH of your soap. They are more expensive than the other alternatives, but if you plan on making more liquid soaps and other homemade cosmetics, or, especially if you want to make soap for gifting or selling, it’s something you could consider buying.

The problem with pH meters is that they usually have some upkeep so if you are only going to use it very sporadically, it may not be the best choice for you.

Testing pH with Red Cabbage

Even before I knew that testing pH with red cabbage was a thing, I accidentally “discovered” its pH reading ability on my own, and used it to my advantage to make a magical, color changing, natural food coloring.

I now know that my magical food coloring can also be used to test the pH of soap!

While I haven’t tried it yet, basically it is said to work like this: Take some cabbage leaves and blend them with a very tiny amount of distilled water, and strain out the leaves to get a purple juice. It will be more concentrated if you use the brightest, thinnest parts of the leaves. Once you have the cabbage juice, you can put a few drops on a small piece of your soap or soap paste. If it turns blue, your soap should be relatively safe to use without irritation for the most part. If it turns green, your soap is probably on the lye- heavy side, and you should consider “neutralizing” it if you plan to use it for face and body.

Should you use pH Balanced “Soaps”?

This is a somewhat controversial conversation…

The argument for pH balanced cleansers

It can be confusing what “pH balanced” is really supposed to mean.

Some pH balanced products fall in a more neutral zone whereas others are made to be more acidic (like our skin).

Of course, real soap will never be neutral or in the acidic range because the soap would break down and separate at lower pH’s. Soap naturally has a higher, more alkaline pH.

When I first wrote this post years ago, I told you that I was one of those people who didn’t believe the hype about using pH balanced “soaps” (really detergents) for skin vs. using soap.

The claim for using pH balanced products is that our skin is more acidic and that alkaline products (like soap) will disturb our “acid mantle,” a covering on our skin that helps protect it. pH balanced products (like syndet bars or shower gels) use other surfactants instead that, unlike soap, can be adjusted into a more acidic range.

Is soap harmful to our skin?

First of all, I’d like to say that our skin isn’t really acidic, per se. Solids and oils don’t really have a pH. You see, as I said above, pH is a measure of the concentration of hydrogen atoms in an aqueous (water) solution. Our skin, though, is covered with acidic secretions like sweat mixed with oils and bacteria. These form part of the acid mantle that protects our skin. If you remove this layer, your body quickly works to replenish it. That’s why, in most cases, we can safely use soap, and our skin completely recovers and becomes more acidic again soon afterward.

That doesn’t mean, of course, that you shouldn’t be careful about what or how you clean your skin. I don’t think that one should overuse soap (or any cleaning agent) of any kind, be it “pH balanced” or not, because you don’t really want to disrupt the skin’s protective layer any more than need be.

My son has atopic dermatitis, and one of the first recommendations of the dermatologist was to not use soap or cleansers of any kind, not even the pH balanced ones formulated for atopic dermatitis, on his skin any more than necessary. I tend to save my soap for washing my hands, or for use in areas of the body where bacteria can grow and cause odors unless I’ve been working out in the garden and need to clean off dirt and grime.

Is pH the real factor?

When it comes to skin, many people either use vinegar (acidic) or baking soda (alkaline) to help soothe skin irritations. (While others find that either can irritate their skin.) Having substances with a pH that is different from your skin isn’t going to necessarily harm it, but if something that is too acidic or too alkaline enough comes in contact with your skin, it can cause skin irritations or even burn you.

So, obviously pH does factor into whether or not something will be irritating to our skin, but, in most cases, most of us should be able to use soap on our skin without any ill effects because our skin recovers from that change in pH pretty quickly.

When should you choose a different surfactant over soap?

Despite what I’ve said above, I do think that there are times that you could (should?) consider other, non-soap, surfactants.

Infant skin is more delicate

When babies are born, their skin has to adapt from being constantly wet in the womb to the dry environment outside the womb. It takes time for their skin to develop the same protective covering as ours. A baby’s skin is more susceptible to irritation from changes in the environment and pH. Because their skin doesn’t recover as quickly as ours, I think it’s better to use another, less alkaline surfactant on their skin. That’s why I developed a pH balanced baby wash and shampoo using mild, natural surfactants for those who are looking for a mild cleanser for their children (or themselves).

Hair, shampoo, and shampoo bars

Our skin is a living tissue that can adapt pretty well to changes in pH, but our hair is a bit more sensitive to harsh changes. Our hair is mostly dead and doesn’t have the same sort of recovery mechanisms.

Because people are looking for a more natural solution to washing their hair, many have turned towards soap-based shampoos and “shampoo bars” that are really just soaps marketed for using to clean your hair. Most people will find, though, that eventually, soap will damage their hair. Its high pH will end up lifting the cuticle of the hair shaft, which can leave hair looking dull and leads to damage. That’s why a vinegar rinse is normally recommended after using a soap-based hair cleanser. The idea is that the vinegar will help reseal the cuticle.

Unfortunately, that may not be enough to prevent damage. I, personally, can’t use soap-based “shampoos” without my hair feeling like straw. That’s why I have shared a few shampoo recipes on the blog like a clarifying shampoo and a shampoo bar.

Laundry soap vs. detergent

Many have chosen to make soap-based laundry “detergents,” but soap-based cleaners may not be the best option for laundry. This is especially true if you have hard water at home. The minerals (mainly magnesium and calcium) in the water react with the soap to form an insoluble substance that can build up on the fibers of your clothes.

This buildup, or “soap scum,” can leave clothes looking dingy over time.

That’s why I usually use my homemade laundry soap for spot removal and use my homemade laundry detergent for daily washing.

Do you really need to test the pH of your soap?

While you normally don’t really need to know the precise pH of a homemade soap that you will be using for yourself, there are a few reasons/times that it may be good to have a ballpark idea of the pH of your soap.

Troubleshooting soap problems with a pH reading

If your soap is cloudy, it may be that it has too many unreacted oils or that the pH is too low, falling towards the neutral range. While a neutral pH might be better for your skin, soap can’t really be effective at a neutral pH. Instead, it has a tendency to fall apart back into its original components. This will leave you with a cloudy mixture that isn’t very good at cleaning.

The other issue with lowering the pH too far is that the mixture would be much more prone to microbial growth. Liquid soap normally has a high pH that makes it an inhospitable environment for most unwanted bacteria and mold. Soap with a higher pH is generally self-preserving.

On the other hand, if your soap isn’t as mild as you would have liked, it may have a pH that is too high. A soap that causes irritation is likely to have unreacted lye and is also likely to have a higher pH. A soap with a pH far enough above 10 will very likely be irritating to most people, and that’s what we’re trying to prevent by “neutralizing” a liquid soap.

How to neutralize a liquid soap

Saying that you are “neutralizing” a soap is a bit of a misleading term, because the goal is not to get the soap into a neutral pH zone. Doing so would inevitably break down the soap. We are really just looking to bring the pH of the soap down slightly.

There are a couple of ways to help bring the pH of a highly alkaline soap down closer to a more neutral range.

Using citric acid to neutralize liquid soap

From reading the ingredients on Dr. Bronner’s liquid Castile soap, it appears that their soaps are neutralized with citric acid.

As a very general guideline, around 4 grams of citric acid should bring down the pH of a Kg of soap paste by around .5. Of course, all of this is highly dependent upon how much water is in your water paste. Because citric acid is, well, acidic, it’s very easy to add too much citric acid, especially with small batches. It’s best to err on the conservative side, adding it little by little. Adding too much will first begin to make the soap look cloudy, and will later cause it to separate. You could, of course, check the pH between additions, but remember that pH readings can be inaccurate.

Unless I was worried that my soap was too alkaline because it was causing skin irritation already, I personally wouldn’t do anything to it. In the case of an irritating soap, though, I would try making a weak solution of citric acid and use it during the second dilution of my soap to gently lower the pH slightly. (Click on the link to read more about how I dilute my soaps.)

If you do see things starting to separate, stop adding the citric acid solution and allow the soap to sit for a while before trying to combine everything back together again. If need be, you can finish diluting the soap with more distilled water.

Using borax or boric acid to neutralize liquid soap

While a lot of people are concerned with the safety of boron-containing substances and avoid using borax or boric acid, it may be the most common way that liquid soap makers in the US neutralize their liquid soap because it is considered the easiest. Plus, it has the extra advantage of helping to thicken your liquid soap, as long as it’s not made with coconut oil or other solid oils. Borax, when dissolved, already has a pH in an ideal soap pH range, so it’s less likely to bring the pH down too far too quickly. Citric acid is a lot more acidic, and it’s easy to go overboard really quickly.

Some countries in Europe have banned boron-containing substances in cosmetic and soap use, so it may not be as common in Europe. It was recently brought to my attention by a friend who used to use boric acid for killing ants and cockroaches that boric acid is no longer sold in pharmacies because the sale to the general public is now illegal here in Spain. I’m not sure if that is true or not, but it does appear that the pharmacy I once bought it from is no longer is willing to sell it. Borax can still be bought from soap making suppliers and other online stores, though.

To neutralize with borax, dissolve 2 parts borax to 3 parts water. So, for example, you could dissolve 2 ounces of borax in 3 ounces of water. Many people say that you should add it when the soap is warm; others say it doesn’t matter. I haven’t done any neutralizing with borax, so I’m not sure if it matters or not.

If you’re wondering about how much to add, I’ve seen it said in several places that you should add 1/2 to 1 ounce of the solution for every pound of soap paste. That said, you should keep in mind that the amount added really depends upon what you are beginning with, and how much you need/want to lower the pH.

If you are trying to lower the pH of your soap and it begins to get cloudy, you should probably stop adding whatever you are using to neutralize your soap.

Last thoughts on pH and neutralizing soap.

This is one of those confusing areas of soap making with numerous opinions and conflicting information.

Because I started making soaps as a “greener,” more biodegradable and less toxic alternative to commercial detergents, I also like to avoid using questionable/controversial ingredients like borax or boric acid, when possible.

I decided to calculate my liquid soaps without a lye excess, at the risk of possibly attaining a cloudier soap, to avoid having to do much in the way of pH testing and neutralizing, and in the interest of simplification.

I’ve spent hours upon hours researching the topic, but I still feel I have a lot to learn. This post is basically sharing my thought on the topic based on research and experimentation up until now, but I’d love to hear what you have to say. I hope that this will at least help you gain a better understanding of the topic overall while you experiment with liquid soap making. Of course, if the thought of making liquid soap scares you after reading all of this (not that I think it should), you could start out with an easy, basic beginner bar soap instead. 😉