Potassium Hydroxide in Liquid Soap: Filing the Saponified Result

Bar soap makers usually know sodium hydroxide, lye, reacts completely during saponification and the finished bar doesn't contain free lye. Liquid soap makers ask the same question about potassium hydroxide, and the answer is the same principle with a different salt. What you're filing isn't the caustic KOH you started with, it's what it became.

What potassium hydroxide actually is and does

Potassium hydroxide (KOH) is the alkali used to saponify fats and oils into liquid or paste soap, the way sodium hydroxide is used for solid bar soap. Potassium soaps stay softer and more soluble than sodium soaps, which is exactly why KOH is the standard choice for liquid castile, liquid hand soap bases, and soft paste soaps. Like sodium hydroxide, potassium hydroxide is highly caustic in its raw form and reacts fully (in a properly formulated and cured soap) with the fatty acids in your oils, leaving behind potassium salts of fatty acids rather than leftover free alkali.

How this shows up on your ingredient declaration

This is the part that confuses new liquid soap makers. You don't typically declare "Potassium Hydroxide" on the finished product's ingredient list the way you'd list, say, a preservative or a fragrance, because it's not present as itself in a correctly made soap. Instead, the saponified result is declared using INCI names that reflect the specific potassium salts formed, which depend on which oils you used.

Oil used	Resulting saponified INCI name (potassium salt)
Coconut oil	Potassium Cocoate
Olive oil	Potassium Olivate
Palm oil	Potassium Palmate
Castor oil	Potassium Ricinoleate
Sunflower oil	Potassium Sunflowerseedate
Shea butter (as a fat source)	Potassium Shea Butterate

If your liquid soap is a blend of coconut and olive oil saponified with KOH, your finished product ingredient declaration reflects Potassium Cocoate and Potassium Olivate, named for the actual saponified fatty acid salts present, not "Potassium Hydroxide" and not "coconut oil" and "olive oil" as raw materials.

What actually needs documenting for your filing

Even though KOH itself typically isn't the final declared ingredient, your formulation records should still show it, because that's your evidence of how the saponification was done and roughly what excess or shortfall you targeted. Soap makers often run a slight fat excess (superfatting) specifically to avoid any residual free alkali, and that's good practice regardless of the notification question. If a batch is genuinely under-reacted and leaves detectable free alkali, that's both a safety issue and a documentation problem, since your finished product wouldn't match what you declared.

Keep records of:

• Oil blend and weights used in each batch
• KOH (or NaOH, if applicable to other products you make) weight and concentration of the lye solution
• Superfat or excess fat percentage targeted
• Any testing you do to confirm the finished product's pH and confirm the absence of meaningful free alkali

Where "true soap" status matters here too

A saponified soap made and sold purely on a cleansing claim, hands-washing, general cleaning, can sometimes be treated differently from a cosmetic in some frameworks, since "true soap" defined narrowly as alkali salts of fatty acids sold only for cleansing is its own category in certain markets. The moment you add a cosmetic claim, moisturizing, gentle on skin, soothing, softening, to that same liquid soap, it becomes a cosmetic and needs to go through cosmetic notification like any other cosmetic product, ingredient declaration and all. A lot of liquid soap brands make exactly this claim (moisturizing hand soap is a hugely common positioning) without realizing it moves them out of "true soap" territory and into full cosmetic obligations.

Filing practicalities for liquid soap makers

If you're notifying a liquid soap that does carry a cosmetic claim, the INCI names for your potassium salts (Potassium Cocoate, Potassium Olivate, and so on) go on the notification with their concentration or concentration range, calculated from your actual formulation, not guessed. Any other cosmetic ingredients you've added, fragrance, humectants like glycerin, botanical extracts, get declared the normal way alongside them.

This is one of the more common places we see makers hesitate on Cosmetic Comply, unsure whether to enter "Potassium Hydroxide" or the saponified INCI names. The saponified names are what belongs on the notification for a properly made, fully reacted soap, and mapping your oil blend to the correct potassium salt names is exactly the kind of translation step the platform is built to handle.