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Potassium Hydroxide in skincare
Saponifier and pH adjuster, consumed by the reaction or neutralized in the finished product. Raw-material hazard, not in-product risk.
Used in shaving creams (rinse-off, AM primarily) and liquid soaps. Like sodium hydroxide, potassium hydroxide in finished, properly saponified products exists as potassium fatty acid salts (soap). NOT as free KOH. Safety is assessed by finished product pH and complete saponification. In cold-process soap making, cure time ensures full saponification. Never use unsaponified or uncured soap products.
What it is
Potassium Hydroxide (KOH, potash lye) is a strong inorganic base used to saponify fatty acids and triglycerides, producing potassium soaps (soft/liquid soaps). As opposed to sodium hydroxide which produces sodium soaps (bar soaps). In shaving creams, KOH reacts with stearic acid, myristic acid, and palmitic acid to form potassium stearate, myristate, and palmitate. The actual soap molecules responsible for lather and cleansing. When properly formulated and fully saponified, no free KOH remains in the finished product. The finished product contains soap salts, not caustic alkali. Undiluted KOH is a highly corrosive chemical causing severe chemical burns. Safety of the finished product is determined by pH (should be ≤10 for rinse-off products) and complete saponification verification. Used alongside or alternatively to sodium hydroxide in soft soap formulations. KOH produces softer, more water-soluble soaps while NaOH produces harder bar soaps.
The facts
| Category | Saponifying Base / pH Adjuster |
| Typical use | Morning and evening |
| Concentration YARAI treats as a full dose | 2% |
| EU maximum permitted concentration | 2.0% ((a) 5% (5) (b) 1. 2% (5) 2. 4.5% (5)) |
| EU Cosmetics Regulation annex | III |
| EU status | restricted |
Why the amount matters, not just the presence
Most ingredient checkers tell you whether something is in the bottle. That is a smaller question than it sounds. Potassium Hydroxide at 2% and potassium hydroxide at a trace level are not the same ingredient in any way that affects your skin.
An ingredient list is ordered by quantity, so position carries real information. YARAI reads that position and scores accordingly, which is why the same ingredient can land differently in two different products.
The honest limit: a list gives order, not percentages. Estimating concentration from position is an estimate. It is a better estimate than ignoring position, and it is still an estimate. We would rather tell you that than let a number look more certain than it is.
Regulatory status
EU CosIng Annex III restricted substance. Max: (a) 5% (5) (b) 1. 2% (5) 2. 4.5% (5)
Common questions
What does potassium hydroxide do in a skincare product?
Saponifier and pH adjuster, consumed by the reaction or neutralized in the finished product. Raw-material hazard, not in-product risk.
How much potassium hydroxide should a product contain?
YARAI treats 2% as a full dose for this ingredient. Below that, the ingredient is present but is scored as contributing less. An ingredient list gives you the order of ingredients, not their percentages, so this is an estimate read from position rather than a measurement.
Is potassium hydroxide restricted in the EU?
The EU Cosmetics Regulation permits this ingredient up to 2.0% in leave-on cosmetics, listed under III. (a) 5% (5) (b) 1. 2% (5) 2. 4.5% (5)
When should I use potassium hydroxide?
Used in shaving creams (rinse-off, AM primarily) and liquid soaps. Like sodium hydroxide, potassium hydroxide in finished, properly saponified products exists as potassium fatty acid salts (soap). NOT as free KOH. Safety is assessed by finished product pH and complete saponification. In cold-process soap making, cure time ensures full saponification. Never use unsaponified or uncured soap products.
Check your own products
Point your camera at a product. YARAI identifies it from the label, finds that product's full ingredient list from published sources, and scores it. No barcode and no box needed, which is how it handles imported and small-brand products.
Concern level, category and thresholds on this page are read directly from the same data the YARAI app scores with, so this page and the app cannot disagree. EU figures cite Regulation (EC) No 1223/2009. Last built 2026-09-09. Nothing here is medical advice.