Every few months someone in a crafting group asks whether they can make soap with baking soda instead of lye, and I always answer gently, because I asked the same thing once. The honest answer is no — but that’s not the end of the story, because baking soda does have a real place in a soaper’s cupboard. Just not the place most people imagine.
- A Crafter’s Honest Look at Baking Soda in Soap
- What Baking Soda Actually Does in Soap
- Materials and Approach You’ll Actually Need
- Key Techniques and Skills
- Skill Level and Time Investment
- Advantages and Challenges
- Real Project Applications
- The Learning Experience
- Comparison with Similar Additives
- Common Questions from Fellow Crafters
- My Personal Results and Insights
- Final Thoughts and My Recommendation
A Crafter’s Honest Look at Baking Soda in Soap
My own baking soda experiment came from a deodorant bar I wanted to make. I stirred a generous spoonful into cold process batter at trace, poured a loaf, and waited. The bars looked fine. They cut fine. And then I washed with one.
The lather was pathetic. A thin, sad froth that collapsed almost immediately, from a recipe that normally produces thick, long-lasting suds. Ten bars, about $15 in oils, and a mystery that took me a proper look at the chemistry to understand.
Baking soda is not lye and cannot make soap. Saponification requires a strong alkali — sodium hydroxide for bars, potassium hydroxide for liquid soap. Sodium bicarbonate is a weak, mild base with a pH around 8.4 to 9.0. There is no version of this craft in which it replaces your lye, and any tutorial claiming otherwise is wrong.
What Baking Soda Actually Does in Soap
Sodium bicarbonate — NaHCO₃, bicarbonate of soda, bicarb — is mined as nahcolite and extracted from trona ore. It’s a single-ingredient compound, and no, it has never contained aluminum, whatever the internet tells you.
The interesting property is that it’s amphoteric: it reacts with both acids and bases. Mix it with vinegar and you get fizz. Mix it with a strong base like sodium hydroxide, and something less obvious happens — it converts into sodium carbonate, which is washing soda.
That conversion is the whole problem. In a pot of cold process batter, you now have two chemical reactions competing for your lye at the same time. Saponification is trying to finish; your baking soda is quietly interfering.
A chemist actually ran this experiment properly. Five identical single-bar batches — a control, plus baking soda and washing soda each added either to the lye or to the oils. Hardness after 24 hours was largely unaffected. And the pH? Baking soda did not lower it at all, which demolishes the most popular claim made about it.
So if it doesn’t soften the bar and doesn’t lower the pH, what’s the harm? The lather. And this is where the data is genuinely damning.
In that same test, the control soap produced around 12 fluid ounces of suds and held them for hours. The baking soda soaps produced about four ounces, and those suds collapsed within half an hour. That’s not a subtle difference — that’s most of your lather gone.
Here’s the detail that fascinated me most. When baking soda was simply added to a solution of finished control soap, it had no effect on the suds at all. The damage comes from making the soap with it — from letting it into the reaction — not from its presence afterward. That tells you exactly where the problem lives.
Which points straight at the solution. Add baking soda after saponification is finished, and you get the exfoliation and the deodorizing without sacrificing your lather.
Materials and Approach You’ll Actually Need
| Item Category | Specifications |
|---|---|
| Baking soda | Pure sodium bicarbonate. Fine, powdery, cheap. Any grocery brand. |
| Baking powder | Do not use. It’s baking soda plus cream of tartar plus a starch, and those extras do unpredictable things. |
| Washing soda | Sodium carbonate. Harsher still, and genuinely not something I’d put on skin. |
| Hot process setup | Slow cooker. This is the method that lets you add bicarb after the lye is spent. |
| Rebatch supplies | Grated cured soap, a little liquid, a slow cooker or double boiler. |
| Usage rate (after the cook) | Start at roughly 1 tsp per pound of oils. Go up cautiously — this is an irritant at high doses. |
| Usage rate (if you insist on CP) | Cap around 5% of oil weight, at 0% superfat, added after trace, with a water discount. |
| Balancing oils | Coconut and castor to rebuild the lather baking soda takes away. Shea to offset the drying. |
| Citric acid | Only if you’re making bath bombs — that’s where bicarb genuinely belongs. |
Baking soda is classified as a skin irritant, and I don’t say that lightly. It’s alkaline, and it strips oils. For dry, sensitive, redness-prone, or acne-prone skin it is a poor choice regardless of what it does to your lather. If you use it, use it sparingly and balance it with something genuinely conditioning.
Key Techniques and Skills
- Understanding that baking soda is an additive, never an alkali — it goes in alongside your lye recipe, not instead of it.
- Using hot process and adding the bicarb after the cook, once the lye has been fully consumed.
- Using rebatch as the safest route: grate cured soap, melt it down, stir in baking soda, mold it.
- Keeping the dose low — a teaspoon per pound of oils is a sensible starting point.
- Sifting the powder so you don’t get chalky pockets in the finished bar.
- Accepting a lather trade-off if you add it to cold process anyway, and compensating with more coconut and castor.
- Dropping superfat to zero and discounting water if you’re determined to use it in cold process at higher rates.
- Never confusing it with baking powder, which brings starch and cream of tartar along for the ride.
- Never confusing it with washing soda, which is harsher and belongs in laundry, not on skin.
- Distinguishing bicarb from soda ash — the white film on your soap tops is sodium carbonate formed when lye meets the carbon dioxide in the air, and has nothing to do with anything you added.
- Testing a single bar before committing a full loaf, because the lather difference is immediately obvious.
- Reaching for bicarb in bath bombs, where it does exactly what it’s supposed to.
The conventional wisdom is correct: add baking soda to hot process soap after the cook, or to rebatched soap — not to cold process batter. By then the lye is gone, there’s nothing left to compete with, and the bicarb is simply suspended in the bar doing its exfoliating, deodorizing job. This is the single practical takeaway of the whole subject.
Skill Level and Time Investment
| Approach | Difficulty | What to Expect |
|---|---|---|
| Rebatch with baking soda | Beginner | Grate, melt, stir, mold. No lye handling. Lather intact. |
| Hot process, added after cook | Intermediate | ~2 hours in a slow cooker. Lye fully spent before bicarb goes in. |
| Cold process, added at trace | Intermediate — with a cost | Works, but expect roughly a third of your normal lather. Cure 4–6 weeks. |
| Bath bombs | Beginner | Bicarb plus citric acid. This is bicarb’s natural home. |
| Replacing lye with baking soda | Impossible | No saponification. You will get greasy paste, not soap. |
Advantages and Challenges
Let me give baking soda its due, because it isn’t useless — it’s just misunderstood. Used correctly, it earns a place.
- Genuinely deodorizing. It nudges skin pH slightly alkaline, which is a less hospitable environment for odor-causing bacteria.
- A fine, gentle exfoliant — much softer than salt, sugar, or ground pumice.
- Costs almost nothing and is already in your kitchen.
- Adds a little hardness to a bar.
- Can soothe itching from bites, and some people find it eases rough, flaky patches.
- Excellent for a gardener’s or mechanic’s bar, where deodorizing and scrubbing matter more than luxurious suds.
- In bath bombs, it’s not optional — it’s the whole engine.
And the honest downsides. It measurably destroys lather when it goes into the reaction. It’s a recognized skin irritant. It makes the bar feel oddly slippery and slow to rinse. And it does not, despite what half the internet insists, lower the pH of your soap — that claim has been tested and it simply isn’t true.
- Reacts with lye in cold process, competing with saponification.
- Converts to washing soda in a strongly alkaline environment.
- Drying for many skin types, particularly dry and sensitive ones.
- Undissolved powder can leave a chalky texture if you don’t sift.
- Endlessly confused with baking powder, washing soda, and soda ash — four different things.
Real Project Applications
The bar I actually make now is a rebatch. I grate about 500 g of a cured, coconut-heavy soap, melt it down with a splash of distilled water in a slow cooker, and stir in roughly a tablespoon of sifted baking soda plus a little tea tree essential oil.
The result is a genuine deodorant bar — mildly exfoliating, quietly effective, and with its lather completely intact, because the lye was spent weeks before the bicarb ever arrived. That’s the version I’d recommend to anyone.
My best use for bicarb is a gardener’s bar. Rebatched soap, baking soda for scrub and odor control, a little ground pumice, and rosemary essential oil. It shifts soil from under fingernails and takes the onion smell off your hands. Six bars, maybe two dollars of materials, and the people I give them to keep asking for more.
If you insist on cold process, here’s the honest formulation. Cap the baking soda around 5% of oil weight, drop your superfat to zero, discount your water, and add the bicarb after trace. Then build extra lather into the recipe — push coconut oil up and keep castor at 5%.
Even then, expect a bar with less lather than a plain one. You are asking the chemistry to do two jobs at once, and one of them will suffer.
Never substitute baking powder. It contains cream of tartar and a starch, and the starch in particular does unpredictable things to a soap’s texture. The bag on your shelf says “powder” for a reason — it’s a leavening blend, not a single compound.
And a clarification worth making, because it comes up constantly. The chalky white film on your soap tops is soda ash — sodium carbonate, formed when unsaponified lye at the surface meets carbon dioxide in the air. It is nothing to do with baking soda, and adding bicarb won’t cause it or prevent it. Spritz the top with 99% isopropyl alcohol at the pour, and it largely disappears.
Where bicarb truly belongs is bath bombs. There, paired with citric acid, it isn’t an awkward addition — it’s the entire mechanism, and it works beautifully. If baking soda is calling to you, that’s the craft it’s asking for.
The Learning Experience
The mistakes here are all conceptual rather than technical. People think baking soda is lye. They think it lowers soap’s pH and makes a bar gentler. They think a little in the batter is harmless.
None of that survives contact with the evidence. The pH doesn’t budge. The lather collapses. And the “gentler” bar is made with a compound that safety references classify as a skin irritant.
The most useful thing I ever did with baking soda was stop trying to make it into something it wasn’t. It’s not an alkali, it’s not a pH buffer, and it’s not a mildness additive. It’s a fine exfoliant and a decent deodorizer. Ask it to do those two jobs and it does them well.
My breakthrough was simply moving it to the end of the process. Same soap, same amount of bicarb, but stirred into a finished rebatch instead of a raw batter — and the lather came straight back. Nothing else changed.
Test a single bar. Make a small rebatch, wash with it, and see whether you even like how baking soda soap feels on your skin. Plenty of people find it drying and abandon the idea entirely, and that’s a perfectly reasonable conclusion to reach after one bar rather than after a full loaf.
Read the actual testing rather than the blog consensus. There is real published work on this — controlled batches, penetrometer hardness readings, pH meters, measured sud volumes. It’s more useful than a hundred posts confidently repeating a claim nobody checked.
Comparison with Similar Additives
| Aspect | Baking Soda | Sea Salt | Activated Charcoal | Kaolin Clay |
|---|---|---|---|---|
| Primary role | Deodorizer + fine exfoliant | Hardener + exfoliant | Detoxifying color, mild scrub | Silky slip, scent anchor |
| Effect on lather | Substantially reduced if added in CP | Reduced at high rates | Minimal | Minimal |
| Reacts with lye? | Yes — converts to washing soda | No | No | No |
| Best method | Hot process after cook, or rebatch | In lye water or at trace | Dispersed in oil, at trace | Dispersed in oil, at trace |
| Skin friendliness | Irritant for sensitive/dry skin | Can be drying in excess | Generally fine | Very gentle |
| Typical rate | ~1 tsp per lb of oils | 1 tsp per lb (or salt bar formulation) | 1 tsp per lb | 1 tsp per lb |
Common Questions from Fellow Crafters
Q: Can I make soap with baking soda instead of lye?
A: No. Saponification needs a strong alkali. Baking soda is a weak base and will not turn oils into soap — you’ll get a greasy, unsaponified mess. There is no lye-free soap from scratch.
Q: Does baking soda lower the pH of my soap and make it gentler?
A: It does not. Controlled testing found no reduction in pH compared to a plain control bar. This is one of the most widely repeated and least accurate claims in the craft.
Q: Why did my baking soda soap barely lather?
A: Because you added it to the raw batter. Testing showed roughly 4 fluid ounces of suds versus 12 for the control, and those suds collapsed within half an hour. Add bicarb after the cook, or in rebatch, and the lather survives.
Q: Can I use baking powder instead?
A: No. Baking powder contains cream of tartar and a starch that interfere with soap texture and chemistry. Use plain sodium bicarbonate only.
Q: Is the white powder on my soap tops baking soda?
A: No — that’s soda ash, sodium carbonate formed when surface lye meets air. Different substance, unrelated cause. Spritz the poured top with 99% isopropyl alcohol to prevent it.
Q: How much baking soda is safe to add?
A: Start at about a teaspoon per pound of oils, added after the cook. It’s an irritant at higher doses, so be conservative — especially in anything intended for sensitive skin.
Q: Does baking soda contain aluminum?
A: No. It’s a single compound, sodium bicarbonate, and it never has. That myth simply refuses to die.
Q: What is baking soda actually good for in this craft?
A: Deodorant bars, gardener’s bars, gentle exfoliation — and bath bombs, where paired with citric acid it does the one job nothing else does as well.
My Personal Results and Insights
| Practice | Outcome |
|---|---|
| Baking soda at trace, cold process | Lather collapsed. Ten bars, ~$15 in oils, all disappointing. |
| Same bicarb, added in rebatch | Lather completely intact. Same soap, same additive, different timing. |
| Gardener’s rebatch (bicarb + pumice + rosemary) | Six bars, ~$2 in materials, my most-requested gift bar |
| pH testing my own bars | No measurable drop from the bicarb. Confirmed what the published testing already showed. |
| Skin trial over several weeks | Noticeably drying on my hands. I now keep the dose low and pair it with shea. |
| Bicarb in bath bombs | Works exactly as intended. This is where it belongs. |
| Biggest lesson | Stop asking baking soda to be lye, a pH buffer, or a mildness additive. Ask it to deodorize and scrub. |
Final Thoughts and My Recommendation
Baking soda has a place in soap making, and it is a modest one. As an additive, after saponification, at a low dose, in a bar meant to deodorize and gently scrub — it works, it costs pennies, and it’s already in your kitchen.
As a substitute for lye, it does not exist. Please don’t let anyone tell you otherwise, and please don’t waste an afternoon and a pot of good oils finding out the hard way.
If you have dry or sensitive skin, I’d honestly skip baking soda altogether. Kaolin clay gives you silkiness without the irritation. Fine sea salt gives you scrub without the lather penalty. There are gentler tools for most of the jobs bicarb is asked to do.
What I take from all this is a lesson bigger than one ingredient. The craft is full of confidently repeated claims that nobody has tested. Baking soda lowers pH. Baking soda makes soap gentler. Baking soda makes lye-free soap. All wrong — and all easily checked, if someone bothers. Be the soaper who checks. It’s the most useful habit you can build.
