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.
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.
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. 
Essential Oils
Essential 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. 
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.
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.
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.
Whether it’s Epsom salt, sea salts, or regular table salt, it is fine to mix salt with Castile soaps. There is no reaction. Salts are good for exfoliation and certain ones such as sea salts or Epsom salt have therapeutic benefits. Salt is much coarser than sugar and should not be used on sensitive skin. Great for elbows and feet, though!
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 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.
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 one carbon atom away from 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.


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

  1. Lisa, you crack me up! Oh, and this article was informative. I know and understand a bit more now. Thanks!

    • Gotta find the fun where you can! And who says chemistry isn’t fun?

  2. This is excellent info! I have wanted to mix in some of my favorite essential oils to get “my” scent, but have been hesitate until reading this, thanks (Sage – Mint Momma).

  3. Great information to have on hand, however, I think your soaps are wonderful and effective all on their own. I use them for just about everything.

  4. I’ve been using (and loving ) your peppermint castile soap for years for hands and body. I wash my hands a lot! What I don’t understand is what property of most plastic dispensers interacts with the diluted soap making it degrade faster and thus losing the appealing smell? Every plastic pump bottle I’ve tried does this; worst of all was a plastic aerating foam dispenser.

    Since I’ve switched to glass containers my peppermint soap stays fresh a lot longer. I’ve tried diluting with filtered drinking water and had the same problem. Once degradation has occurred in a plastic container, the container is no good anymore. However, in the shower I’d much prefer a plastic container.

    The degradation does not occur in the plastic bottles the soap comes in. What’s going on?

    Thank you!

    • Hi Carol – There are so many different types of plastic. Some definitely degrade more quickly than others. Some are more photosensitive than others – resulting in faster degradation in sunlight. Glass probably insulates better than plastic as well. I agree that plastic is a better option for the shower. I keep an 8 oz. Dr. Bronners bottle in the shower and refill that from a gallon I keep under the sink. That way I’m sticking with plastic that I know. For more info on our use of plastic, check out this article: https://www.drbronner.com/about/our-earth/packaging-innovations/.

  5. I’ve tried mixing certain essential oils to the castile soap, and it actually made the soap thick/bar-soap like. Which essential oils work best?

    • Hi Blayne – One thing to keep in mind with essential oils is to verify that they are pure, and not mixed with some sort of carrier oil or other substance. That could create an entirely different chemical reaction. The most common ones I add to the soap are Citrus and Tea Tree, but considering I’ve named two of the scents we make anyways, that’s hardly surprising. I know people add extra Peppermint, Lavender, Patchouli…

      I invite other readers to comment with their favorite oils to add to the soaps!

  6. Extremely informative. Now I know why my mixture of Olive Oil, salt and the soap came out weird and with a funky after-smell. 🙂

  7. Yep, I am embarrassed to say I have tried them all.
    However, I must say adding a bit of bleach (don’t use often) to the Sal suds in my white laundry, just seems to boost the “whiteness”.
    From now on, Sal suds only! Promise!

  8. I think you should mention that some people react badly to essential oils. I tried your shaving gel and it burnwd my face so badly I had to wash it off.

    • Hi Dr. F – There certainly are sensitivities to essential oils. That is why we have our Unscented (light blue) line of products.

  9. Thank you very much for this post, I have been using your liquid and bar soaps for 9 yrs now, I love it
    Nen Sorensen

  10. Very nice format and article. About borax: it’s a mineral, sodium borate, so isn’t really biodegradable. It’s often mixed with biodegradable ingredients and the labelling may be misleading as to the biodegradability of the mixture. I’m also unclear about its sustainability, because it’s mined (hence the 20-mule-team association).

    Small amounts of boron can be beneficial to plants, such as fruits in the rose family, but quite toxic in larger amounts. For this reason, I’ve avoided using borax in houses with septic and/or gray water systems.

    • Thanks for the heads up, Susan! We’ve had those buttons disappear before. We’re working on figuring out where they went.

  11. Great tips and reminders of what NOT to do. I think with the trend of the cleaning videos on YouTube, you have people just mixing whatever and calling it natural when you should really just stick to the basics that you have provided over the years – I love your YT videos Lisa!

    • Thank you for the kind words, Lauren! Glad they’re helping. I know everyone’s heart is in the right place, and are trying to do the right thing by mixing stuff together, but I absolutely agree – keep it simple!

  12. Over time, I’ve started using Castile Soup mixed with water for almost all cleaning in my house. However, I have noticed something when I use it in a spray bottle for the counters (and now I use the spray bottle for quick dish washing too). For some reason it makes me (and anyone who comes around while I’m spraying it) cough. Like it kind of gives a choking feeling. I still use it because I know it’s safer than other products, but can you tell me why it’s giving this choking/cough feeling? Am I using too much – or should it not be used in a spray bottle? Just wanting to confirm it is safe used this way. Also, another question, completely different topic – I sometimes mix castile soap, water, and baking soda as a shampoo for my hair. The article says that combo is great for cleaning grime and laundry, is it maybe a mixture I should be using on my hair? I don’t use it every wash, but do use it occasionally when I’m trying to cut out harsh chemicals in my beauty routine (at one point in time I did use it every wash for 6-8 months).

    • Hi Tiffany – Putting it in a spray bottle is perfectly fine. Our lungs by nature reject any foreign vapors and so if you breathe in soap vapors, your lungs are going to object. It could be spray bottle is vaporizing the spray a little too much. See if you can adjust the nozzle to make more of a targeted spray rather than the really misty spray.

      For the shampoo, that mixture of soap, water and baking soda sounds fine. You’ll likely need a vinegar rinse afterwards.

  13. How much essential oil would be necessary to scent a 16oz bottle of castle soap?

    • Hi Linda – It entirely depends on the essential oil. Some are more potent than others. Start with maybe 5 drops and shake it up and give it a sniff. Increase from there.

  14. thanks for posting! Some good tips I didn’t know. I do adore adding essential oils to my Dr Bronners Castile, as well as sea salts for exfoliation. in case anyone is interested, I also like diluting it with a bit of distilled organic rose water for my personal care uses. Very gentle and seems to have a softer effect on my sensitive skin after rinsing than when diluted with the water from the tap.

  15. Thank you. I am in love with my general cleaner that involves water, peppermint castile soap, and peppermint essential oil. You made me laugh with the vodka story/recipe.

  16. Your pages are amazing. You totally go oppositely the so called norm I gather that you are a chemist. Love love your insight.

  17. Hello,

    I love reading your posts. It has been recommended that I mix 5 oz of unscented castile soap with 5 oz of raw honey for a face and body wash. I would like to know your opinion on this. Thank you.

    • Hi Rebecca – I am intrigued! I am curious to know the purpose of the honey. There is no chemical reaction between the soap and the honey, other than the soap would grab hold of the honey to rinse it away. I’m not sure if combining them at equal volumes, there might not be enough soap to clean anything else off the face. I’d be willing to try it just to see. You could try it on your hands or something first just to see how it feels and how it rinses.

    • The lady who uses this formula is in her 80’s and is Dutch. She said it leaves her skin really soft. Her daughter and family also use this.

      I actually bought the sugar soap and really am enjoying it.

      Thank you for replying.

  18. Hello. Great post! I really like Dr Bronner’s. How can I wash dry, brittle hair, with Castile soap, without doing it out? Thanks!

    • Hi Paul – Check out this definitive hair washing guide from the Dr. Bronner’s blog. The Castile may not be the best option for you. Instead, try the Organic Sugar Soap or even the Organic Shave Soap for hair washing.

  19. Hi!
    I didn’t see citric acid on the list, I’m just curious about that one. I notice it in a lot of household cleaners. Would it be beneficial in any way making a shower cleaning spray with castile soap, water, and citric acid?

    • sorry – one more question as well. If i wanted to boost my laundry, while using castile or sal-suds as the laundry soap. would I be able to use either baking soda or oxygen bleach powder as a booster?

    • No problem! Baking soda works with both the Castile and the Sal Suds. Check out details about that in the post above. Oxygen bleach powder, of which Oxyclean is an example, isn’t good with either. This is a combo of washing soda (sodium carbonate) and hydrogen peroxide. Hydrogen peroxide is pretty unstable, and the alkalinity of both the Castile and Sal Suds would just break it down. It would be a waste.

      If you really like using the oxygen bleach powder, however, you could do a presoak and rinse of your laundry and then wash them with the Castile or Sal Suds.

    • Hi Kc – Thanks for asking! I’ll add it to the list. It’s a no-go for the same reason that vinegar or any other acid doesn’t work. Acids react with the Castile soap, which is alkaline, and break it down.

      A savvy reader might raise a hand here and point out that there is already citric acid in our soap. What’s up with that?! We individually test each batch to make sure there are no unused sodium hydroxide molecules running around in it, which would be irritating to the skin. We add the exact amount of citric acid to catch any stray NaOH. Any more citric acid, though, would snag the soap molecules themselves.

  20. I got the shave soap. And, it’s great! 2 questions: If washing a beard, with the shave soap; do you recommend using the rinse? Also, is the shave soap gentler than the baby bar? Thanks!

    • Hi Paul – The shave soap is fantastic for washing beards. It draws in extra moisture than our castile – bar or liquid – does. Because it contains that shikakai extract (what makes it so dark brown), it really softens the hair, and the skin as well. I’m actually writing a post this very day about beard care, of all the people I have talked with, none have used the rinse. Many wash with our Sugar Soap (the Shave Soap is an even thicker and more nourishing Sugar Soap) and then they use our unscented Magic Balm for smoothing and control.

  21. Hi,
    In interested in combining part distilled water castle soap with jojaba oil and grapseed oil. I straight razor shave and relater and do at least 3 passes. The last pass is an oil pass to clean up the remaining stubble.
    How to i combine the water oils, and soap? I’m not looking for a real explosion of foamy suds at all. Just a very thin clear slick formula.

    • Hi Mike – I apologize for my delayed response here. With what you’re striving for, you can definitely combine the soap with water and oil, and give it a good shake before each use. It won’t suds much – possibly not at all, but it will give you that slick feel you’re looking for. As far as ratios go, maybe start with 1:1 on the water and soap, let’s say 1/4 c. of each, and add 1/2 tsp. of each of the other oils? That’s a starting point. Feel free to adjust to your liking.

  22. Thank you so much for this thorough and organized explanation. This information is very helpful for DIYers just starting out and natural makeup/skincare enthusiasts.

  23. Hi Lisa – so grateful for your blog and all the pure gold you’ve put here. Thank you! I’m about to order some Sal’s Suds and can’t WAIT. Question: if I mix hydrogen peroxide with Sal’s Suds, is that a safe combo? (I’m attempting to make some homemade laundry detergent with Sal’s Suds and some homemade bleach which uses hydrogen peroxide. I know this list was primarily addressing castile soap…not sure if Sal’s Suds applies to all of these in the same way?) Thank you!

    • Hi Grace – I’m so glad it has been a help to you. I haven’t tackled all the chemistry yet as thoroughly for the Sal Suds and mix-ins. I do know that hydrogen peroxide is pretty unstable and breaks down into water fairly quickly in the presence of an alkali, which the Sal Suds is. My guess would be no, it’s not a useful combination. I will look into this with Dr. Vartan and see what he says.

    • Hi Sherlei – I appreciate your patience. To answer your question we had to do some testing. There is no reaction between the castile soap and colloidal silver.

  24. This is great, thanks! Could you share any thoughts on mixing water and castile soap, in an anti-microbe sense? Should there be a preservative added as well seeing as water can so easily breed germs? I’ve been researching for a while and am so confused on the topic of using water in DIY products. Thank you.

    • Hi Catherine – I have never had an issue with water causing a problem with microbes. That being said, theoretically it is possible, based on the cleanliness of water used and how long the solution sits. In our litigious society, most people are going to cover their backsides by mentioning the possibility. Tap water in the U.S. is exceedingly clean of microbes – usually the problems with it lie in the other direction with excessive chlorine and such. I don’t worry about the microbes, and I use RO water to get rid of the additives. I have never added a preservative to DIY solutions. Soap is naturally self-preserving, and that will keep most dilutions safe for as long as it would take you to use them up. However, if you wanted to, you could add a couple drops of vitamin E, which is a natural antioxidant. Or use distilled water.

    • Hi Janelle – How frustrating! There shouldn’t be a reaction when adding essential oils to Castile soap. Sometimes when that happens, we’ve found that the essential oils used aren’t pure oils. Can you give me a few more details about the essential oil you added – were there any other ingredients in it except pure tea tree and lavender essential oils?

  25. I am so happy and relieved to read these rock solid facts from you and Dr. Vartan Libaridian. Now I’m going to educate a slew of DIY cleaning bloggers 😀

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