Dr. Bronner's

What Can You Mix with Castile Soap?

What can you mix with Castile soap - Dr. Bronner's Castile Soap carton

Over the years I have received an extraordinary range of questions about mixing stuff with our Castile soaps. There’s a lot of creative thinking going on out there.

But before you get busy with your green self, let me remind you:

Chemistry happens.

As a general rule, do not mix household cleaners together, especially if you do not understand the ingredients. To the best of our knowledge the chart below outlines what we expect to happen based on tests.

I know that you want to toss together your favorite Green-It-Yourself (GIY) ingredients and hope everybody gets along. But sometimes they don’t.

I am not a fan of complicated mixtures. I don’t do complicated. Just give me some Castile soap with an occasional dash of baking soda or essential oils and send me on my way. However, just because I’m not a fancy girl, don’t let me hold you back.

Helping me here is Dr. Vartan Libaridian, Dr. Bronner’s chemistry and R&D consultant. The chart below gives you both my lay analysis and Dr. Vartan’s scientific breakdown.

IngredientLisa BronnerDr. Vartan
Alcohol (aka isopropyl alcohol, the other IPA)Alcohol is an antiseptic which is commonly used among other things to clean needle sites or cleanse wounds (ouch!). I get that someone might want to take one cleaner (soap) and another cleaner (alcohol) and put them together to make one super cleaner. Better to do a one, two punch: wash with the soap and then spray with the alcohol. This is also the CDC’s recommendation for cleaning and disinfecting.
The overall cleaning effect of soap is not affected, at least up to 5% of IPA. Above that concentration, there is a dramatic decrease of foaming, the solution becomes cloudy, and the alcohol interferes with micelle formation. Although IPA increases slightly the cleaning capability of the soap, it also kills the foaming effect of the Castile Soap. It is a fine line. I would recommend not to add more than 5% of alcohol in the blend. This applies to all alcohol containing products: vodka, cognac, Ethanol, IPA, …
Aloe Vera
If you picture “aloe vera” as an enticing green gel, you have been grossly misled. The real thing is slimy and turns mustard yellow and stains like nobody’s business. That being said, pure aloe applied to skin straight from a plant provides highly effective sunburn relief. However, when I combined the Castile with just a bit of the pulp inside my aloe frond, it gelatinized the whole amount of soap. Think “mucousy.” Very unappealing. Better to apply aloe vera after you wash. Aloe vera has at least 75 active ingredients including saponins, vitamins, amino acids, salicylic acid. However, adding this material either in powder or in solution (gel) form to the liquid soap does not give the soap any added value. The brief contact of the liquid soap with aloe vera on the skin will not leave any aloe residue, and aloe requires prolonged contact to do its work.
Baking soda
Baking soda adds a soft abrasion to the cleaning power of the soap, which makes it a good scrubber for grimy sinks and laundry. In laundry, it is a whitener and deodorizer. It also buffers the Castile Soap, protecting it from acidic substances that might affect its pH.
I don’t know why you would want to combine the Castile Soap with bleach. If you’re using the Castile in an effort to be safer, you’re undoing that effort by adding bleach, which causes everything from obstructive lung disease to burns to environmental contamination. Hypochlorite                 Soap
NaClO     +          R-(CH2)n-COOK
pH 12-13                   pH 9-9.5

When blended, Na [sodium] displaces K [potassium], thus creating R-(CH2)n-COONa. This is a hard soap formula. This doesn’t last too long, and eventually it dissolves. In summary, the soap stays as soap, with both K and Na soap coexisting, but at a higher pH. It can be irritating to the skin.
Borax is an effective cleaning agent, but I don’t like it. Combining it with Castile Soap doesn’t change this. Borax is praised because it is sustainable and biodegradable and old. But it is not non-toxic. It is irritating to the skin, dangerous if inhaled, and has been linked to reduced sperm count in men and reduced libido in women. It should be kept well away from children and gloves should be worn when handling it. Borax may have some beneficial effects when combined with Castile Soap. It has a pH of 9.3, similar to that of the soap. It buffers the Castile Soap, protecting it from acidic substances that would break it down, thus helping the cleaning process. 
Castile SoapCombining Castile Soaps is a fantastic thing to do to achieve your perfect scent. All the soaps in our Castile line have the same soap base with different essential oils added, except for the unscented, which has a higher ratio of saponified olive oil. My dad had his “Euco-Peppo Bear Wash,” a blend of Dr. Bronner’s Peppermint and Eucalyptus which he used for washing our dogs. A favorite blend of mine is Citrus & Almond.
Citric AcidUsually the thought behind adding citric acid to Castile Soap is to bring down the pH. However, acid will react with the soap itself and break apart the soap molecule. You’ll be left with an oily mess. “But your ingredients list citric acid!” Yes, we add carefully apportioned amounts of citric acid in order to catch any unreacted hydroxides from the soap making reaction. Adding any more citric acid than we’ve already added will reverse the reaction.
Coconut milk
This combo is all about making a more moisturizing shampoo. It does reduce the cleaning ability of the soap because some of the soap molecules are busy chasing the oil molecules in the milk, but there can still be some cleaning power available. See notes on “Oil” below.
Club Soda
I’m not really sure of the goal of combining this with castile. Maybe because I suggest using club soda to clean windows. Once again it’s the idea that if each are good then both together must be better. Not really though.
Total waste of money and time. The addition of carbonated water at pH 3-4 with soap will release Carbon Dioxide. Nothing else. Bubbling soap. Very unstable. 
Epsom SaltEpsom salt is magnesium sulfate and has a range of therapeutic benefits. However, it is slightly acidic, which brings us back to the idea of acid/base reactions. (See my post, A Word of Caution About Vinegar & Soap.) Soap is a base, aka an alkali. Because of this Epsom salt does react with Castile soap. It is not a dangerous reaction, but it undoes the benefit of both substances. Use them separately. Not together. Epsom salt is not compatible with Castile Soap. Magnesium sulfate (Epsom salt) has a slightly low acidic pH, around 6. The Castile soap has a pH of around 9. Adding the magnesium sulfate reverses the soap and releases the fatty acid, producing visible flakes of oil.
Essential OilsEssential oils have a lot to add to cleaning solutions both for personal care and for house care. They can give you a personalized scent and add therapeutic qualities. Avoid the trap of thinking that if a little is good, then more is better. Some essential oils are pretty potent. Do research on each type, as they have very distinctive properties.
Any essential oils can be added. They might cloud out the Unscented Baby Mild Soap.
Whether you’re looking to thicken the soap or make it smoother, keep in mind that the soap already has naturally occurring glycerin in it. More glycerin doesn’t increase the efficacy of the soap, but if it makes you happy, go for it.
Adding glycerin increases moisturization potential of the soap, but above 2-3% it decreases foaming properties.
Hydrogen peroxide
Hydrogen peroxide is a little misleading, all coy and subdued in its modest brown bottle. It’s a mild antiseptic on cuts and has an abundance of other uses. But when a chemist uses the word “explosive”…

Combining these two doesn’t boost the effectiveness of either. Another myth of thinking if both are good, together they’d be better. They’re not.
This material can be dangerous if the customer uses concentrated hydrogen peroxide (30% concentration or higher). Mixed with Castile Soap, it releases oxygen. If there is a heat source next to it, it can be explosive. Usually, the hydrogen peroxide that is used to clean wounds is at 3% concentration. In this case, the danger is minimal. When mixed with the soap, the hydrogen peroxide brings no antibacterial benefit. Hydrogen peroxide is acidic so any contact with alkaline soap will cause it to dissociate into water and oxygen. You are basically destroying the peroxide molecule. 
Lemon juiceLemon juice is an excellent addition to your green cleaning toolbox, but like vinegar (see below), not a good partner for soap. The acidity of lemon and other citrus juices quite literally undoes Castile Soap – a process we call unsaponification. The resulting goopy mess renders the soap ineffective at best, an oily mess at worst. While citrus juices are pulled from the pulp, are water-based, and acidic, citrus essential oils are extracted from the rind of the fruit, are oil-based, and are pH neutral. They do not react with the soap and are great additions.
I am intrigued by the discussion of oatmeal face masques, dry shampoo, and exfoliators. I had no idea. There is no problematic reaction in blending oatmeal with Castile Soap. My only concern is clogging the plumbing. If I do try a face masque or some such, I’ll rinse it off in the kitchen with the garbage disposal.
Oil – Jojoba, olive, or coconut The idea here is to make the soap more moisturizing. I get that. But keep in mind that soap grabs hold of oils. This is its primary purpose. So if you add too much of any oil, then the soap is going to be busy chasing the oil you’ve added instead of the grime on your body. For deeper moisturizing, wash with the soap and moisturize afterwards.Any of these oils can be added. They make the soap superfatted, which means it contains oil that has not been turned into soap. More than 0.5% – 1% is not recommended.
OxycleanThis is another effort to give the castile an added boost. Oxyclean is a combination of hydrogen peroxide (see above) and washing powder (see below). Might as well just reach for the washing powder.This is another effort to give the Castile an added boost. Oxyclean is a combination of hydrogen peroxide (see above) and washing powder (see below). Might as well just reach for the washing powder. Oxyclean contains hydrogen peroxide and sodium carbonate. Hydrogen peroxide as stated earlier will be dissociated into oxygen and water. No benefit.
Sodium carbonate will be useful in softening the water. 
Sal Suds with Castile Soap
I’m not sure why you would want to do this. Again, it’s the idea that if both are good separately, then together they must be even better. It’s unnecessary, but chemically speaking there are no adverse effects. Although there is no interaction between the 2 entities, I don’t see any beneficial effect. For sure Sal Suds is more aggressive on the skin.
Chemically speaking “salt” is a category, not a specific substance. However, most people are thinking of “sodium chloride” which is common table salt, and the base of Sea Salt. Castile Soap does not react with sodium chloride, and mixing the two together can make a great exfoliating scrub. Since salt is coarser than sugar, do not use this on sensitive skin. Great for elbows and feet, though. As a category, “salt” is the result of reacting an acid and a base. Soap itself is another kind of salt, as is Epsom salt (see above for reaction).Salt increases the viscosity of the Castile Soap to a certain extent.
Sugar is a natural humectant, which means that it draws moisture into our skin. This is why we use it in our Organic Sugar Soaps. You can make a lovely scrub by mixing it with Castile Soap.
Here’s a whole post I wrote about this one way back in 2011. Vinegar and Castile soap are great separately and terrible together. They’re like the siblings who just can’t leave each other alone. They get all in each other’s business. Vinegar un-saponifies soap. It’s not dangerous, just messy, and ruins the cleaning ability of either. The one caveat is if the soap is buffered by something like baking soda, as in this GIY Soft Scrub recipe.
Vitamin E (tocopherols)
Mixed tocopherols – aka vitamin E – is perfectly fine to mix with Castile. These are the antioxidants we use in our soaps. For personal care, vitamin E is usually recommended for anti-aging properties. For house care, mixed tocopherols is an antioxidant in GIY solutions. Either way, it’s fine to mix with the Castile Soaps to make a solution last longer.
The first time a friend told me she used vodka to clean her house, I thought that would definitely make housework more fun. However, she put in a spray bottle, not in a glass. While alcohol is an antiseptic, the concentration of drinking alcohol is not high enough for cleaning. If you decide to use it, see the above section on mixing it with Castile. I can think of better uses for vodka.
I did not specifically mix soap with vodka, since this is not a common material that I carry in the lab. (See discussion on alcohol)
Washing soda
Washing soda, or sodium carbonate, is similar to its culinary cousin Baking Soda, or sodium bicarbonate. This is a common ingredient in homemade laundry detergents. Washing soda acts as a water softener as well as a powerful scouring agent. If you are cleaning heavily soiled laundry like towels or work clothes, this will help you a lot. However, it can be a bit harsh, so I do not recommend using much on regular loads, and definitely not on delicates. It combines just fine with Castile soap.
What about a recipe calling for baking soda AND washing soda AND borax? Well, yes, this will scrub your clothes excellently but I hope you like to go shopping because this will wear down your clothes exceptionally fast.
There is benefit to adding sodium carbonate when you have hard water. In this case sodium carbonate precipitates calcium carbonate thus improving the soap’s cleaning capabilities.

Further reading

Why Vinegar & Castile Soap Don’t Mix Well

How Soap Works

13 Essential Green Cleaning Ingredients

Sal Suds or Castile Soap – Which To Use?

Download Now!

Castile Soap Cheat Sheet

Dilute! Dilute! OK! But how much? Print this guide!


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Lisa Bronner says:

Hi Jennifer – That is a superb idea. I have added it to my task list to get that up here.

Chris says:

Is it safe to mix Sodium Carbonate with essential oils? I want to make a natural multi-purpose cleaner/degreaser using Sodium Carbonate, grated Castile soap and essential oils. There is a company in the UK that make powdered multi-purpose/degreaser that you dilute to spray bottles the ingredients are pretty simple Sodium Carbonate, Sodium Olefin and Multicomponent Fragrance I am going to replace the Sodium Olefin with Castile soap do you think it would work any advice would be much appreciated.

Lisa Bronner says:

Hi Chris – There is no reaction between these ingredients. Let me know how it goes!

Katrina Witt says:

Hi Lisa – Any thoughts on mixing Castile soap with honey? I mixed it 1:1 in a regular pump bottle and the pump didn’t clog. It also seemed to lather like crazy but that could be my imagine since I wasn’t doing a side-by-side comparison. My skin feels softer after a shower with this combination. Oh, and it does smell like dirty, stinky socks. I call it Stinky-Sock Soap/Shampoo. However, when I step out of the shower, all I smell is CLEAN! I’d love to hear what you think!

Lisa Bronner says:

Hi Katrina – Wow! Well, there is no problem with mixing the Castile soap and honey. Honey, as a sugar, works as a humectant, drawing moisture into the skin, so this explains the smoothness that you feel. And there is no reaction between the two products. So far as the Stinky-Sock part, goodness! That doesn’t sound pleasant. All of the Castile soaps have the same base with different essential oils, or no essential oils in the case of the Unscented. Perhaps one of the other scents would meld better with the scent of honey? I think Almond would be lovely or perhaps Citrus.

Melissa Noble says:

I have bought Castile soap to make my own laundry soap. I have tried just a single drop to wash my hands. I felt it was very drying to my skin. I thought this was supposed to be the opposite. Please, help understand.
Thank you

Lisa Bronner says:

Hi Melissa – Which Castile soap did you buy? While Dr. Bronner’s Castile soaps all have the same soap base, the different essential oils have different impacts on the skin. The Peppermint, for example, can be more drying, which is great for people with normal to oily skin. The Lavender or Unscented are milder. For laundry, though, all of the Castiles work equally well. My Green Laundry Care video and article may be a useful guide.

Tyrone says:

I know that Castile soap is an excellent insecticide, but I am hoping to create an effective herbicide also by mixing in a small amount of citric acid. While I’m aware that this will break down the soap molecules, I believe that this is necessary to have weeds coated in the released oils. Can you tell me if I’m on the right track?

Lisa Bronner says:

Hi Tyrone – You are right that you’d be coating the leaves in the released oils, but I do not know if this is effective on weeds. If coating the leaves with oils is beneficial to eliminating weeds, you could probably then save yourself the step and use olive oil or coconut oil without the soap/citric acid combo.

Melissa says:

Thank you for doing this article! I’ve found a DIY stain remover for laundry and bleach alternative mix that both required 3% hydrogen peroxide and 1 a baking soda the other a washing soda..I was able to look it up before doing either one to be sure they would mix ok

Lisa Bronner says:

Hi Jazz – No, these two shouldn’t be mixed. Since soap is an alkali, it would react with the acid.

Lisa Bronner says:

Hi Chase- No, boric acid is an acid. It will react with the Castile Soap, an alkaline, and cause it to unsaponify.

Rae says:

I am using your Castile soap in a foaming soap dispenser, diluting with water 10:1. It works very well, but the mixture tends to separate, with the soap falling to the bottom of the dispenser. I have read that adding cetyl alcohol as an emulsifier might help, and apparently it also moisturizes your skin, increases foaming, and is safe to use. However it dissolves in oil but not in water. Is this a good idea, and is there a way to make it work?

Lisa Bronner says:

Hi Rae- I’m glad your foaming pump is working well! Since soap is readily soluble in water, it would not separate. I think perhaps what you are observing at the bottom of the dispenser is the result of a reaction between the soap and the minerals in hard water. This reaction forms a harmless white precipitate that does not impact the soap’s ability to clean. If you want to avoid this precipitate and have a clearer solution, use filtered or distilled water. However, it is purely an aesthetic decision, and not necessary. I have not looked into the impact of cetyl alcohol on the soap. I will look into that and get back to you.

doreen says:

I am so happy to stumble upon this site! Bookmarked to come back to. I make laundry powder w/combination of castile soap, baking soda, washing soda, sea salt, citric acid & oxygen bleach. I have been experimenting w/ratios of all ingredients but haven’t found one definitive recipe I like best. Your thoughts on this? Are all necessary? I’ve been doing my own powder and cleaning products for over 15 years now and love the results but don’t want to overdue it if not necessary. Thanks for any feedback!

Lisa Bronner says:

Hi Doreen- Welcome! I’m glad you’re finding my site helpful. Regarding your laundry soap formulation, while all of the ingredients have cleaning properties on their own, some of them when mixed will react with each other. Others in the bunch are duplicating each other.

Citric acid, when it dissolves in water will form an acidic solution which will react with several of the other ingredients which are alkalis, namely baking soda, washing soda, oxygen bleach, and the soap. I don’t know which one it would react with first, but in any case, it would be neutralized and not be available to add cleaning power to your laundry. The mixture is likely still working for you because there are still plenty of available ingredients even after the citric acid neutralizes some of them.

Oxygen bleach is made of sodium percarbonate, which when dissolved in water becomes hydrogen peroxide and sodium carbonate, the chemical name of washing soda. This means you have two sources of washing soda in your mixture. Baking soda, washing soda, and oxygen bleach all do the same thing in increasing power of intensity. They all are boosters which add scrubbing power to the laundry. I recommend using just one of them. I like to start with the least intensive option, which would be baking soda with its much lower pH (8, as opposed to 11 for the washing soda) and then only increase it if needed. I think this makes fabrics last longer.

In addition to leaving out the citric acid, I recommend leaving out the sea salt. Salt is reputed to stop colors from running, but this is only an issue with new fabrics. Salt can also help with stains, but only when directly applied to them and allowed to sit before laundering. Salt can also corrode the metals of your machine.

I know it sounds super simple, but when I use the grated Castile soap, I mix it only with baking soda. Because I have hard water, I add vinegar to the fabric softener compartment as a rinse aid. If you opt to use washing soda with the grated Castile, this would also act as a water softener and the vinegar would not be necessary.

About Lisa Bronner

My grandfather was Dr. Bronner, my family makes soap, and I share ways to use it plus tips on greener living.

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Castile Soap Cheat Sheet

Dilute! Dilute! OK! But how much? Print this guide!