Sodium Hydroxide (Lye): How to List It on Soap Notifications

New soap makers almost always ask the same question the first time they sit down to fill out an ingredient list: does sodium hydroxide go on the label? The short answer is usually no, and the reason why trips people up more than the answer itself.

What actually happens to the lye

Sodium hydroxide, CAS number 1310-73-2, is the strong alkali that reacts with fats and oils in cold process soap making. That reaction is saponification, and it is not a light mixing step, it is a full chemical conversion. The sodium hydroxide combines with the fatty acids in your oils and, when the batch is properly formulated and cured, none of it remains as free lye in the finished bar. What you're left with is soap, meaning the sodium salts of those fatty acids.

That is why a correctly made and cured bar of cold process soap does not list "sodium hydroxide" on its ingredient panel. It lists the saponified oils themselves, using INCI names that reflect the finished salts, such as:

Oil used	INCI name on label
Olive oil	Sodium Olivate
Coconut oil	Sodium Cocoate
Palm oil	Sodium Palmate
Castor oil	Sodium Ricinoleate
Shea butter	Sodium Shea Butterate

If your recipe uses potassium hydroxide instead of sodium hydroxide, typically for liquid soaps, the naming convention shifts to "potassium" versions of the same terms, like Potassium Cocoate.

Why this matters for your filing

If your soap only makes a cleansing claim, it may qualify as true soap and sit outside standard cosmetic notification requirements altogether. But the moment your bar makes a cosmetic-style claim, moisturizing, gentle on sensitive skin, softening, anything beyond plain cleansing, it becomes a cosmetic and needs a Cosmetic Notification Form filed through the Cosmetic Notification System, with every ingredient listed by INCI name and a concentration or concentration range, within 10 days of first sale.

When you're filling that form out, list the saponified oil names, not raw sodium hydroxide, because that reflects what is actually present in the finished product. Listing raw lye as if it survives into the bar is not just unnecessary, it is inaccurate, and accuracy is the whole point of the exercise. The notification is meant to describe what a consumer is actually exposed to.

There is a narrow exception worth knowing about: if your process leaves excess unreacted lye, which happens with poorly balanced recipes or under-cured batches, that is a formulation problem before it is a labeling problem. A soap with detectable free alkali is a safety issue, not just a paperwork one, and it's worth testing pH and running proper cure times regardless of what you eventually put on the label.

Handling lye safely, briefly

This is a compliance blog, not a safety manual, but it is worth saying plainly: sodium hydroxide is caustic and reacts exothermically with water. Always add lye to water, never the reverse, work in a ventilated space, and wear eye protection and gloves. None of that changes your labeling obligations, but a burn injury will absolutely change your week, so it is worth the reminder.

Superfatting and trace amounts

Many recipes intentionally use slightly less lye than the stoichiometric amount needed to saponify all the oil, a practice called superfatting, so that a small percentage of unreacted oil remains for skin feel. That leftover oil is a real, measurable ingredient and should appear on your list at its actual concentration, distinct from the saponified portion. This is one of the more common accuracy gaps in soap labels: makers list "olive oil" as if the whole amount survived unreacted, when in fact most of it saponified and only the superfat percentage remains as free oil.

Keeping your filing consistent

If you sell several bars from the same base recipe with different scents or colors, each variant technically needs a filing that matches its actual formula, though minor variants can often be handled as amendments to an existing notification rather than fresh filings. Getting the INCI naming right on the first filing saves you from having to unwind a wrong entry later, especially once you're managing a handful of SKUs derived from the same core saponified oil blend.

Cosmetic Comply was built partly for this exact wrinkle. It takes your actual recipe, maps each oil to the correct saponified INCI name and CAS reference, flags anything that looks like it needs a second look, and lets a real compliance reviewer confirm it before the notification goes out.