Do You List Lye and Sodium Hydroxide on a Soap Label

This question comes up in nearly every soap maker forum sooner or later, usually phrased with real anxiety: "I use lye to make my soap, do I have to put sodium hydroxide on the label, and will that scare customers who think it means there's lye in the bar?" The short answer is it depends on what's actually in your finished bar, and understanding why clears up a lot of the confusion.

What actually happens to lye during soap making

Sodium hydroxide, lye, reacts with fats and oils in a chemical process called saponification. That reaction converts the lye and the oils into soap and glycerin. If your recipe is properly formulated and cured, there's no meaningful free sodium hydroxide left in the finished bar. The lye did its job as a reactant and it's gone, chemically transformed into something else entirely.

This is genuinely different from an ingredient like a preservative or a fragrance oil that goes into the product and stays there in its original form. Lye's whole purpose is to react and disappear.

So does it go on the label or not

Because sodium hydroxide is consumed during the reaction and isn't present as itself in the finished product, many soap makers don't list it as a finished-product ingredient, and instead list the fats and oils used in the recipe, since those are what remain (as soap) in the bar. Ingredient labeling conventions in various markets have historically allowed listing the saponified oils rather than "sodium hydroxide" plus each individual oil, since that reflects what's chemically present in the final product.

That said, labeling conventions and expectations differ by market and can change, and this is exactly the kind of detail worth confirming against your specific target market's current labeling guidance rather than assuming one market's convention applies everywhere. If you're selling into more than one country, check each one rather than copying a label format from a market you're not actually filing in.

Where this gets genuinely tricky: superfatted soap

If your recipe is superfatted, meaning you intentionally use less lye than needed to saponify all the oil, so some oil remains unreacted in the bar for moisturizing effect, that excess oil is present in its original form and should be reflected accordingly in your ingredient declaration. The lye itself is still fully consumed (assuming your recipe and cure process are sound), but the unreacted "superfat" oil is a real, present ingredient, not a byproduct, and needs to be accounted for like any other ingredient still physically in the product.

What this means for your CNF or other notification

If you're filing in Canada, your Cosmetic Notification Form should reflect what's genuinely present in the finished soap. This is a case where getting expert input, from an experienced soap-making community, a formulator, or your target regulator's guidance directly, matters more than guessing based on habit. A batch that wasn't fully saponified, whether from a measuring error or too short a cure time, could have some residual lye, and that's a real safety issue completely separate from the labeling question.

Where "true soap" status matters

There's a related but distinct question here: whether your product counts as a "true soap" (an alkali salt of fatty acids sold purely on a cleansing claim) or as a cosmetic. If your soap makes no claims beyond cleansing, it may be treated differently than a cosmetic in some markets. The moment you add a cosmetic-type claim, moisturizing, anti-acne, softening, gentle on sensitive skin, you've likely moved it into cosmetic territory regardless of how you handle the lye question, and the rest of cosmetic labeling and notification rules apply.

A practical checklist

1. Confirm your recipe is fully saponified with a proper cure time before assuming no free lye remains
2. Decide whether your soap is superfatted, and if so, account for the residual oil in your declaration
3. Check your specific target market's current labeling convention for saponified soap rather than assuming
4. Be honest with yourself about whether your marketing claims have pushed the product from "true soap" into cosmetic territory

If your soap has crossed into cosmetic territory through its claims, or you're ready to notify it as one, Cosmetic Comply can match your saponified oils and any added ingredients to their correct INCI names and screen the whole formula before filing, currently for the Canadian market.