How to Make Baby Soap: Buttermilk Bastile Baby Bar (Buttermilk Powder + Zinc Oxide)

One of my favorite soap recipes of all time is my Buttermilk Bastile Baby Bar that you can find on a guest blog post over on I love the way this soap feels on my skin.

I received an email recently about wanting to make the soap with coconut milk instead. You can substitute the buttermilk with any milk of your choice, goat milk, almond milk, coconut milk…etc. I happened to have some powdered buttermilk on hand so decided to make a batch with that.

I also decided to add some zinc oxide. Zinc oxide is great for irritated and itchy skin.


So first of all, why do I call it bastile? Castile is soap that is traditionally made using 100% olive oil. Bastile is a term coined by soapmakers before me for soap that is almost 100% olive oil, but not quite. It typically has 10-30% other oils and butters.

The high amount of olive oil makes it a super nourishing and mild soap, perfect for baby!

Baby Buttermilk Soap

A word of warning if you make this soap, and especially if you give it as gifts: This is not a tear-free soap. The soap will burn eyes if it gets into them during the bath. Keep the soap away from baby’s eyes.

Buttermilk Bastile Baby Bar Recipe with Zinc Oxide

Olive Oil – 360 grams (75%)
Coconut Oil – 120 grams (25%)

Water – 120 grams
Lye – 66 grams
Buttermilk Powder – 1 tablespoon
Zink Oxide – 1 tablespoon

(No fragrance or essential oils in soap for baby.)

Safety Warning: This recipe is for soapmakers who have a basic knowledge of the soapmaking process and know the correct safety procedures to use when handling lye. If you are new to soapmaking, visit our beginner instructions. Be sure to wear safety goggles and gloves while soaping.

Step 1 – Make your lye solution and set aside to cool down.

Step 2 – Weigh the coconut oil into a microwave container. Melt, just until melted.

Step 3 – Add the olive oil to the melted coconut. This helps to cool the temperature down.

Olive Oil Soap

Step 4 – Add the buttermilk powder and the zinc oxide to the oils. Stir to get rid of any clumps.

soap with buttermilk

Step 5 – Once the oils and lye are cooled to under 100 degrees F, pour the lye into the oils and mix to trace.




Step 6 – Pour into your mold.


zinc oxide soap

Step 7 – Allow to sit overnight to saponify. After 24 hours unmold your soap and cure for a minimum of 6 weeks.

baby soap recipe


Happy Soaping!

Amanda Gail

About the Author:

I am a soapmaker, author and blogger! I started blogging in 2008, sharing soap recipes, design tutorials and publishing articles on various topics of soapmaking.


  1. ElliottSmall March 5, 2018 at 11:18 pm - Reply

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  2. Aide Mancera February 27, 2018 at 10:22 am - Reply

    Hello, Amanda, l am new at soapmaking, I love your web page… thank you so much for share with us…. About this recipe, can I use powder goat milk instead of buttermilk? and for a big batch, can I doble this recipe? Thank you. Regards from Mexico.

  3. dhanalakshmi January 30, 2018 at 1:19 am - Reply

    how much range of PH for Buttermilk Bastile baby bar.

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  5. lisa October 18, 2017 at 9:28 pm - Reply

    I would probably make it either HP or CPOP .. both force the gell stage & making the soap quicker to use..
    any changes in the recipe.. ( I wouldn’t think so 🙂 )

    • Kim Nguyen November 13, 2017 at 8:58 pm - Reply

      Where do you get zinc oxide

      • Amanda Gail November 14, 2017 at 9:21 am - Reply

        Not sure, probably Bramble Berry or Wholesale Supplies Plus. Lots of suppliers have it.

  6. Lynn September 29, 2017 at 5:09 pm - Reply

    I’m new to soaping. I made this soap the first time and let it go to gel phase and it turned a light brown. The second time I made it the temperatures for the lye and oil were lower between 75 and 85 degrees when i combined. I refrigerated it overnight. 12 hours later it was still very soft in the mold so I put it back in the fridge and it’s still soft, but I was able to take it out and slice it. I tried the zap test and it zaps….does it just need to sit longer? Thanks in advance for your help!

    • Wallis Ann Lahtinen-Hicks September 29, 2017 at 10:05 pm - Reply

      soap will take longer to get hard because of the high olive oil content, also seems to take longer in silicone molds-Always assuming your measurements were accurate and your followed directions carefully : D!

      • Lynn September 30, 2017 at 1:35 pm - Reply

        Thanks for responding. I’ll wait it out then!

  7. Jenni June 28, 2017 at 8:07 pm - Reply

    When i recalculate the recipe on soapee and soap calc i get different figures to yours, what is your superfat and what is you lye to water ratio please amanda

  8. bergor June 3, 2017 at 9:27 pm - Reply

    hi. Amanda. .I new in soap making . would like to try our baby soap making.. can i use breast milk instead of water for the lye solution. and how much ?

  9. Gen January 29, 2017 at 4:38 pm - Reply

    Can I use kaolin clay in place of the zinc oxide? Is kaolin clay still a safe option for babies?

  10. Mary Harbor December 20, 2016 at 7:19 pm - Reply

    Did you add the zinc oxide simply to whiten the soap?

    • wallis l hicks December 21, 2016 at 7:43 am - Reply

      Zinc oxide is also skin soothing. It’s used in various medications for conditions like psoriasis and excema. It’s not used as a medication in soap but it is supposed to be soothing to delicate or irritated skin

  11. Nora August 10, 2016 at 12:49 pm - Reply

    Hi Amanda,

    This is a great recipe for making skin-safe soap for babies. Can we also use sustainable palm oil as a percentage of the carrier oils? We are hoping that if we did we can get a harder bar of soap in a shorter curing period. We are definitely going to try this though. Thanks!

  12. Danuta June 14, 2016 at 9:20 am - Reply

    I made it , just added 5% of castor and it looks so good, white, the unscented. It seems that the soap with that high Olive oil amount needs a bit longer cure. I am going to try to keep it for at least 10 weeks. What do you think Amanda?
    I love your blog so much thank you,:)

  13. Trish May 11, 2016 at 4:14 am - Reply

    Can u use this recipe for melt and pour

  14. Wallis February 22, 2016 at 7:00 pm - Reply

    I made a couple of batches of this with fresh buttermilk, modified a bit by adding in some castor oil(because I like castor oil in everything soapy), didn’t use zinc oxide b/c I didn’t have any on hand and added a bit of scent. I love this soap and how it lathers-so creamy!

    • Sudha January 2, 2018 at 6:35 pm - Reply

      At what stage did you use fresh buttermilk?

  15. LIndsay February 3, 2016 at 10:51 pm - Reply

    I’m new to soapmaking so forgive me if this is a stupid question. Everything I have read says the lye and oils should be much warmer than in the instructions above (where you say 100F). Why so cool?

  16. Sadia January 10, 2016 at 3:55 am - Reply

    what was the superfat/water reduction at?

  17. Sadia January 10, 2016 at 3:55 am - Reply

    what was the superfat/water reduction at?

  18. Anna January 10, 2016 at 2:59 am - Reply

    Hi Amanda,

    A few weeks ago I made this soap, but using yoghurt powder instead of buttermilk. It still have to wait till it reached its 6 weeks of curing, but from what I can see so far it looks like a great soap!

    I have allowed myself to post this modified recipe on my blog
    I have referred in this blog post to your original recipe. I hope you do not mind!
    This is the post:

  19. Cee December 31, 2015 at 1:55 pm - Reply

    Ronna, I just tell customers, “Don’t let the soap get in the baby’s eyes!” LOL

  20. Ronna December 30, 2015 at 10:49 pm - Reply

    I am sure this soap is great for baby’s skin, but how is it for the eyes. I have many requests for “tear free” version. Lets face it cold process soaps can burn the eyes. What can be done to elevate that problem without messing up the soap recipe?

    • Amanda Gail January 4, 2016 at 9:47 am - Reply

      Hi Ronna – I have a warning paragraph in the tutorial that it will sting eyes. You’ll have to educate mamas that it will sting and to not get it in baby’s eyes. Makers of tear free shampoos add chemical numbing agents. As handcrafted soapmakers who are wanting to make a more natural product, that’s just not something that I want to do. So educating the end user is very important.

  21. alison December 25, 2015 at 8:08 pm - Reply

    If I want to use fresh buttermilk instead of powder ,how would I do that? Thanks for this post.

  22. Mervat December 22, 2015 at 1:47 pm - Reply

    Hi could I use any butter insted of butter milk powder… thank y

  23. Cee December 21, 2015 at 10:30 am - Reply

    Amy, you can check the “Best by” date on the container.

    • Amy December 25, 2015 at 9:06 am - Reply

      It was from bramble berry. It came in a bag. No date labeled for use by.

      • Amanda Gail December 26, 2015 at 7:24 pm - Reply

        Oh no! No batch code or anything? Since it is dry, I would bet it lasts awhile.

        • Amy December 31, 2015 at 7:59 am - Reply

          it smells just fine, but BB says to only keep it a year. It’s been kept in a cool dry area. It smells fine, so I’m using it.
          In the future it would be nice if everything was labeled.

  24. Amy December 20, 2015 at 5:45 pm - Reply

    Hi amanda,
    How long does buttermilk powder last for, and would it smell funny if it was rancid?

  25. Anne-Marie Faiola December 17, 2015 at 5:20 pm - Reply

    I am so glad you love the recipe and mold! (We do too!) These soaps really are great for anyone looking for something for sensitive skin. =)

  26. Cee Moorhead December 16, 2015 at 4:13 pm - Reply

    I found this recipe over at Bramble Berry… made it with goat milk powder… loved it! The mild silky lather is not just for babies! As long as it’s left unscented, it’s great for dry, sensitive skin, mature skin, and for cancer patients under-going radiation treatment. Thank you SO much for sharing this, Amanda!

  27. Dori Martz December 16, 2015 at 1:06 pm - Reply

    What are you using for the molds? I am looking for a mold to use for making small individual sized lotion bars. These look like the size for which I am looking. Thanks

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