What Can You Mix with Castile Soap?

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.

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.

 Bronner MomDr. Vartan
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.
Bleach
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
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.
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.
Glycerin
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. 
Oatmeal
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. Per Dr. Vartan’s analysis, add no more than ¼ - ½ tsp (1.25-2.5 mL) per 1 cup (250 mL) of soap. 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. 
Rubbing 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. Although not a dangerous combo, it doesn’t add much benefit. I wouldn’t do it.
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 and the solution becomes cloudy. 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, …
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.
Salt
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
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.
Vinegar
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 Castiles to make a solution last longer.
Vodka
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. There is some wisdom in this because any alcohol is an antiseptic. As far as mixing it with Castile, see the above section on alcohol. 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.

88 thoughts on “What Can You Mix with Castile Soap?

  1. I’m late to this party – but better late than never :D…what about manuka honey? Could that be safely added to castile soap? Thanks!

  2. Hi Dr. Bronner,
    I added Neem oil to Castile soap in my Ortho Dial-N-Spray container, and the mixture turned into a gelatinous mess with the consistency and appearance of caulk. Ruined my Dial-N-Spray plus I lost about $25 of oil and soap. I was trying to kill bugs on my lemon tree.

    It was not until I read down through the comments on this page that I realized a lot of people had similar problems when they mixed in various oils. I think your instructions need to be more up front and tell people to exercise a lot of caution if they try to mix in oils, rather than tell them that oils are ok.

    https://www.lisabronner.com/what-can-you-mix-with-castile-soap/

    • Hi MJ- I’m really sorry that happened to you! Pure neem oil with a neutral pH shouldn’t have this reaction with our Castile soap. I’m following up with our chemist on this one. In the meantime, was the neem oil you used pure, raw oil or was it blended into something?

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