Guides / Sodium hydroxide on the label

Do I have to list sodium hydroxide on a soap label?

Published 22 September 2026; rules last checked 25 September 2026. A labelling reference, not legal advice.

Under the plain words of Article 19(1)(g), yes: the list is made "in descending order of weight of the ingredients at the time they are added", and sodium hydroxide is an ingredient you add. Under the convention most soap makers and many suppliers follow, the list names what the lye becomes instead: "Sodium Olivate", "Sodium Cocoate", with "Glycerin" and "Aqua", and the word "Sodium Hydroxide" does not appear. Both readings circulate in EU and UK artisan practice, both account for the lye, and neither allows it to be dropped as if it had not been used. Our tool prints the as-made list and tells you that it did.

What the text says

Article 19(1)(g) requires a list of ingredients, and for that purpose defines an ingredient as "any substance or mixture intentionally used in the cosmetic product during the process of manufacturing". Only two things are excluded: impurities in the raw materials, and "subsidiary technical materials used in the mixture but not present in the final product". Lye is intentionally used, and it is not a subsidiary technical material; it is the reagent that makes soap. The order is "descending order of weight of the ingredients at the time they are added", with ingredients below 1 % allowed in any order after those above it, and Article 19(6) requires the glossary name for each, which for lye is "Sodium Hydroxide" (entry 26674).

The two readings, side by side

For a plain olive and coconut soap, the same recipe reads two ways:

The as-added list describes what went into the pot, by input weight, with every name from the glossary. The as-made list describes the bar: the sodium salts of the fatty acids (glossary entries 26872 and 26507), the glycerin the reaction releases, and the water that remains. In the second reading the lye is present in the names of the salts, which is why it is an accounting choice rather than an omission. Listing the oils and the salts together, or leaving lye out of an as-added list, is neither reading and is the version that goes wrong.

Why the tool prints the as-made list

Our soap engine saponifies the oils a recipe marks as soap and prints the salt names, because that is what the bar contains and what most makers, suppliers and safety assessors expect to see on a soap label. It prints the salts and the water; it does not add a "Glycerin" line, because it does not model the glycerol the reaction releases, so makers who follow that part of the convention add it from their own figures. It keeps a note beside the result saying that the text's own wording supports the as-added reading, so the choice is made in the open. For a leave-on or rinse-off product that is not soap, nothing saponifies: the oils keep their botanical names and a lye line is flagged, never silently consumed. If your safety assessor or an authority asks for the as-added form, the recipe you entered is the list: the oils, water and lye in the order of their weights.

Elsewhere

• Great Britain. Article 19 of the assimilated regulation carries the same words, so the same two readings. The names are the same too; the entry numbers on this page are the EU glossary's, and the glossary Great Britain kept from the EU lists the same names under other numbers.
• United States. A bar that meets the soap definition in 21 CFR 701.20 and is sold only as soap needs no ingredient list. A bar sold as a cosmetic lists its ingredients "in descending order of predominance" under 21 CFR 701.3(a).

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