Potassium Hydroxide (KOH): The Maker's Guide to Liquid Soap and pH Balancing

Potassium hydroxide (KOH), also called caustic potash, is a strong alkali used mainly to make liquid and soft soaps and to adjust the pH of cosmetic formulations. In simple terms, it reacts with oils to turn them into soap, and a tiny amount can nudge a product's acidity or alkalinity to the right level. Azlok supplies it as white pellets at 85% purity, from a handy 100 gram jar up to bulk 20 kg packs.

What potassium hydroxide is used for

KOH is the sister of sodium hydroxide (lye). While sodium hydroxide gives you hard bar soap, potassium hydroxide produces soap that stays soft or liquid. That single difference makes it the go-to alkali for a specific set of jobs.

• Liquid and paste soap: Body washes, hand soaps, shaving soaps and shampoo bases start as a KOH-oil reaction.
• pH adjustment: Formulators use very small quantities to raise pH in creams, gels and cleansers so the product performs and stores well.
• Cleaning and degreasing: It cuts through grease and grime in industrial and household cleaners.
• Soap and detergent production: A core raw material in commercial formulations.
• Agriculture and food processing: Used in specific processing steps and pH control.

How to use it in soap making

Making liquid soap follows the same logic as bar soap, but with KOH and a little extra water. Here is the broad method most makers follow.

1. Run your numbers. Always put your oils through a reliable lye calculator set to KOH, and factor in the 85% purity. Never guess the amount.
2. Mix the solution. Slowly add the pellets to cold water \u2014 never water to pellets \u2014 in a heat-safe container. It will heat up and fume, so work in a ventilated area.
3. Combine with warm oils. Blend the lye solution into your oils and stir or blend to "trace", then cook the paste until it turns translucent.
4. Dilute and rest. Dissolve the finished paste in hot water to your chosen strength, then let it settle and clear for a few days before bottling.

For pH adjusting, you typically make a dilute KOH solution and add it drop by drop, checking with pH strips or a meter until you reach your target.

Safety you should not skip

Potassium hydroxide is caustic. It can cause serious burns to skin and eyes and gives off heat and fumes when mixed with water. Treat it with the same respect you would give any strong chemical.

• Wear chemical-resistant gloves, safety goggles and long sleeves every time.
• Work in a well-ventilated space and avoid breathing the vapours.
• Always add pellets to water, slowly, using cold water to limit the heat spike.
• Use glass, stainless steel or HDPE containers \u2014 never aluminium, which reacts with alkali.
• Keep vinegar or plenty of running water nearby to rinse accidental splashes.
• Keep away from children and pets. Do not ingest, and never leave it in an unlabelled container.

Finished, properly cured soap is safe and gentle \u2014 the caution applies to the raw pellets and fresh lye solution.

Buying and storage tips

KOH is hygroscopic, which means it grabs moisture straight from the air and can clump or turn to slush if left open. Buy a pack size that matches how quickly you will use it \u2014 the 100 gram or 500 gram jars suit hobbyists, while small businesses may prefer the 1 kg or larger bulk options for better value.

• Store in a tightly sealed, airtight container, ideally the original packaging.
• Keep it in a cool, dry place away from acids, moisture and direct sunlight.
• With correct storage the pellets carry a 24-month shelf life.
• Check the COA and MSDS Azlok provides so you know exactly what you are working with.

FAQ

What is the difference between potassium hydroxide and sodium hydroxide?

Both are strong alkalis used in soap. Potassium hydroxide (KOH) makes soft and liquid soaps, while sodium hydroxide (NaOH) makes hard bar soaps. They are not interchangeable in a recipe.

Can I make liquid soap without potassium hydroxide?

Not true soap-from-scratch. Liquid soap made by saponification needs KOH. You can buy ready-made soap bases if you would rather skip working with lye.

Why is the purity listed as 85%?

Commercial KOH commonly runs around 85% to 90% because it absorbs moisture. Set your lye calculator to this purity so your recipe stays balanced and your soap is not lye-heavy.

Is potassium hydroxide safe on skin?

Raw KOH is caustic and can burn skin, so it must never touch you directly. Once it has fully reacted and cured into soap, it is safe and mild for washing.

How should I store leftover pellets?

Reseal them immediately in an airtight jar and keep them somewhere cool and dry. Exposure to air causes clumping and slowly reduces their strength.