What Is Soda Ash on Cold Process Soap—and Is It a Problem?

If you’ve ever made or purchased cold process soap and noticed a white, powdery film on the surface, you might have wondered what it is. Is it mold? Is the soap still safe to use? The good news: that white layer is something called soda ash, and it’s completely normal—and harmless.

What Exactly Is Soda Ash?

Soda ash is the result of a natural chemical reaction between sodium hydroxide (lye) and carbon dioxide in the air. When freshly poured soap batter is exposed to air—especially during the first 24 to 48 hours—it can form this white coating on the surface. It’s especially common in soaps that aren’t insulated or that are poured at cooler temperatures.

Does It Affect the Soap?

Not at all. Soda ash is purely a cosmetic issue. It doesn’t change the way your soap lathers, cleanses, or feels on your skin. The soap is still completely safe and effective to use.

Can You Prevent It?

While you can’t always avoid soda ash entirely, there are a few things soapmakers can do to minimize its appearance:

• Spraying the top of the soap with rubbing alcohol right after pouring helps reduce the reaction with air.
• Covering or insulating the mold can help maintain warmth and prevent ash from forming.
• Using a water discount (slightly reducing the water content) can also help limit soda ash.
• Gelling the soap—encouraging it to go through the gel phase—can help create a smoother top.

That said, many soapmakers embrace soda ash as a sign of a truly handmade product.

Can You Remove It?

Yes! If you prefer a cleaner look, soda ash can be gently washed off with water, steamed off, or even wiped with a damp cloth. However, if you love the rustic, handcrafted look of a little ash on top, there’s no need to do a thing.

The Beauty of Handmade Soap

At the end of the day, soda ash is just one of the many little quirks that come with handmade, cold process soap. It’s a natural part of the process and a visual reminder that your bar wasn’t mass-produced in a factory—it was crafted by hand, with care.

So next time you see that delicate white film on your soap, you can smile, knowing it’s perfectly normal and part of the charm of truly artisanal skincare.