Liquid Castile Hand and Body Wash: Recipe, Formula and Method

A liquid Castile hand and body wash is a gentle, pourable soap made from olive and castor oils, perfect for pump bottles at the sink or in the shower. It is also a cosmetic product, so the moment you sell it in Great Britain it must comply with the UK Cosmetic Products Enforcement Regulations 2013 and the retained Regulation (EC) No 1223/2009, overseen by the Office for Product Safety and Standards. This guide gives you the full formulation, the method, and a clear path to selling it legally.

This recipe is part of our maker series. If you want a wider library of tested formulas across skincare, hair care and more, our 100 Beauty Formulas cosmetic formulation guide collects one hundred professional formulations in one place.

How liquid soap is different from bar soap

Bar soap is made with sodium hydroxide, but liquid soap is made with potassium hydroxide, usually shortened to KOH. That single change makes all the difference. Where sodium hydroxide produces a hard bar, potassium hydroxide produces a soft, translucent, honey like paste that dissolves in water. You cook the paste to drive the reaction to completion, then dilute it into a smooth, pourable wash. This is why liquid soap making is sometimes called the hot process method.

An olive oil led recipe gives a gentle, Castile style wash, mild enough for hands and body, while a little coconut oil adds cleansing power and castor oil gives a rich, stable lather. The reward for the extra effort is a beautiful, honest liquid soap with an ingredient list you can be proud of.

• Gentle and versatile. One wash for hands, body and even a foaming dispenser when diluted further.
• A honest ingredient list. Real soap made from named oils, not synthetic detergents.
• Economical. A batch of paste dilutes into a large volume of finished wash.

A safety word before you start

Potassium hydroxide is a corrosive alkali, exactly like sodium hydroxide, and demands the same respect. Treat it as a hazardous substance and follow the Health and Safety Executive guidance on the control of substances hazardous to health (COSHH), along with the safety data sheet supplied with your KOH. The essential rules are:

• Wear goggles, gloves and long sleeves whenever you handle the KOH or the raw soap.
• Work in a well ventilated space, away from children and pets.
• Always add the KOH to the water, never the other way round, as it can react vigorously.
• Keep white vinegar to hand for surface spills, and rinse skin contact with plenty of cool water.

Equipment you will need

• A digital scale accurate to one gram
• A slow cooker or a heavy pan for the hot process
• A stick blender to reach trace
• Heatproof jugs and a silicone spatula
• A thermometer
• A large pot or jug for diluting the paste
• Goggles, chemical resistant gloves and an apron

The liquid Castile formulation

This makes a concentrated soap paste that you then dilute. Amounts are by weight, and you must verify them in a liquid soap calculator set to potassium hydroxide, accounting for the purity of your KOH, which is usually around ninety percent.

Verify before you make it. Liquid soap uses potassium hydroxide, which has its own saponification values and is usually only about ninety percent pure. Always run the recipe through a liquid soap calculator before mixing, and set a small superfat of around one to three percent.

Distilled water only. Use distilled water throughout. The minerals in tap water can cloud the finished soap and shorten its life.

Preservation is essential. A hard bar is anhydrous, but a diluted liquid wash is mostly water and can grow bacteria, yeast and mould, so it needs a broad spectrum preservative added at the level your supplier recommends. This is one of the first things a Cosmetic Product Safety Report checks for a water based product, so do not skip it.

How to make it, step by step

Liquid soap takes a few hours, most of it hands off cooking time, so it is a good weekend project.

1. Prepare

Wear goggles, gloves and long sleeves, work in a ventilated space, and weigh every ingredient before you begin.

2. Make the lye solution

Sprinkle the potassium hydroxide into the distilled water, stirring until dissolved. It heats and fumes briefly, so do not lean over it, and set it aside.

3. Cook to a paste

Combine the warmed oils and the lye solution, blend to trace, then cook gently in a slow cooker for two to four hours, stirring occasionally, until the mixture becomes a thick, translucent, amber paste that looks like petroleum jelly.

4. Test for clarity

Check the paste is fully saponified by dissolving a small amount in a little hot water. A clear or only slightly cloudy solution means it is done. A milky, separating solution means it needs more cooking.

5. Dilute

Weigh the paste, then add two to three times its weight in hot distilled water. Leave it to dissolve, stirring now and then, until you have a smooth, pourable soap. Warmth and patience do the work here.

6. Preserve, scent and bottle

Once fully cooled, stir in your preservative at the correct level, then any fragrance, adjust the thickness to taste, and bottle into pumps or foamers.

Understanding superfat in liquid soap

Superfat behaves differently in liquid soap than in a bar. In a bar, a five percent superfat leaves conditioning oils in the soap. In a liquid soap, too much free oil makes the finished wash cloudy and can leave an oily film, so liquid soap is usually made with a very small superfat of around one to three percent, or even zero, and gentleness is added back through the choice of oils and a touch of glycerin. This is another reason to run your recipe through a dedicated liquid soap calculator rather than guessing at the numbers.

Getting a clear, professional liquid soap

If you want a clear rather than cloudy wash, three things help. Use distilled water throughout, cook the paste fully so every oil is saponified, and consider a small amount of a sequestering agent, which binds any stray minerals that would otherwise cloud the soap. Cloudiness is not a safety problem in itself, but a clear, well finished soap looks more professional on the shelf. Let the diluted soap rest for a day or two, as some cloudiness settles out on standing.

Choosing the right preservative

Not every preservative suits soap. Liquid soap sits at an alkaline pH, so you need a broad spectrum preservative that stays effective in those conditions, added at the exact percentage your supplier specifies. Add it once the soap has cooled, since heat can weaken some preservatives, and never rely on fragrance, essential oils or vitamin E to preserve a water based product, because they simply do not. Getting the preservative and its level right is one of the most important safety decisions you will make.

Dilution, thickening and preservation

Dilution is a balance. Too little water leaves a thick, slow soap, while too much leaves it watery. Start on the thicker side, since you can always add more water. If you want a thicker wash, a small amount of salt solution can thicken some liquid soaps, though a high castor recipe like this is naturally rich.

Because your finished wash contains water, preservation is not optional. Choose a broad spectrum preservative suitable for the pH of soap, add it at the supplier level, and keep everything scrupulously clean during making and bottling. This protects your customers and is central to passing a safety assessment.

How much finished wash does this make?

This is where liquid soap becomes very economical. The paste from this recipe weighs a little over a kilogram, and once diluted at two to three times its weight in water it yields roughly three to four kilograms of finished wash, enough to fill many pump bottles. Because you dilute to taste, you can make a thicker hand wash or a thinner foaming wash from the same batch of paste. Store any undiluted paste in a sealed tub and dilute more as you need it, which keeps the concentrate stable and lets you make fresh wash on demand.

From hobby to brand: your first steps to selling

Turning a recipe you love into a product you can sell is an exciting step, and it is more achievable than many makers think. The practical order is simple. Finalise and record your formula with exact percentages and your supplier details, keep clear batch records, and note your dates from the very first batch. Then have the product safety assessed to obtain your Cosmetic Product Safety Report, build your Product Information File, appoint a Responsible Person, notify the product, and get your label checked before you print. Phoenix Safety Consultants can handle the entire regulatory side from start to finish, so you can focus on making beautiful products while we make sure they are ready, safe and legal to sell.

Labelling your wash for sale

A liquid wash is a cosmetic and needs a full label under Regulation (EC) No 1223/2009. The ingredient list uses INCI names, and for liquid soap the saponified oils appear as their potassium salts, such as Potassium Olivate, Potassium Cocoate and Potassium Castorate, alongside Aqua, glycerin, your preservative and any fragrance allergens over their thresholds. A label and packaging review makes sure the list, the preservative and the warnings are all declared correctly.

Troubleshooting common problems

• Cloudy paste that will not clear. It may need more cooking, or the recipe was lye heavy. Test a diluted sample and cook longer if needed.
• The wash is too thin. Dilute with less water next time, or thicken gently following your calculator guidance.
• Separation over time. Usually a dilution or preservative issue, and exactly what a safety assessment is designed to catch.
• A cloudy finished soap. Often caused by tap water. Use distilled water throughout.

Variations

• Foaming hand wash. Dilute a little further and use a foaming pump for a light, airy lather.
• Lavender or citrus. Add a skin safe fragrance within its limits for a scented wash.
• Extra gentle. Raise the olive oil and lower the coconut for the mildest possible Castile wash.

From kitchen to shelf: selling your body wash legally

Handmade body wash is a cosmetic, so the moment you sell it, it must meet UK and EU cosmetic law before it goes on the market. Here is what compliance involves.

• A Cosmetic Product Safety Report. Every cosmetic sold in the UK or EU needs a Cosmetic Product Safety Report (CPSR), a formal safety assessment signed by a qualified Safety Assessor under Regulation (EC) No 1223/2009. If you make several variants, they can be assessed together as a range through our multiple variant CPSR service.
• The full document set. Alongside the CPSR you must hold a Product Information File, and your product must be notified. Our all in one compliance package covers the CPSR, PIF, SDS and notification together.
• Notification. Before sale, your product is notified in Great Britain through the Submit cosmetic product notifications service (SCPN), and in the EU through the CPNP, which we handle in our CPNP product notification service. It is declared under the correct frame formulation, a liquid soap, so your exact recipe stays private.
• Responsible Person and labelling. Every product needs a Responsible Person who is legally accountable to the authorities, and a compliant label. Phoenix can act as your UK and EU Responsible Person and carry out a label and packaging review.
• Selling in the United States? Under the Modernization of Cosmetics Regulation Act, the US Food and Drug Administration now requires facility registration and product listing for many cosmetics, which we manage through our FDA MoCRA listing service.

When you are ready to take your body wash to market, contact Phoenix Safety Consultants and we will guide you through every step.

Frequently asked questions

Why does liquid soap use potassium hydroxide?

Potassium hydroxide makes a soft, dilutable soap paste, whereas sodium hydroxide makes a hard bar. That is the fundamental difference between liquid and bar soap.

Does homemade liquid soap need a preservative?

Yes. Once the paste is diluted with water, the wash can support microbial growth, so it needs a broad spectrum preservative added at the recommended level.

Is liquid Castile soap gentle?

Yes. An olive oil led recipe gives a mild, Castile style wash that suits hands and body, though a little coconut oil helps it lather.

Why is my liquid soap cloudy?

Cloudiness is often caused by tap water minerals or a paste that was not fully cooked. Use distilled water and cook the paste until a diluted sample runs clear.

Do I need a CPSR to sell liquid soap?

Yes. Any cosmetic sold in the UK or EU needs a Cosmetic Product Safety Report, which for a water based wash looks closely at preservation, plus a PIF, a Responsible Person and a compliant label.

About the author

This article is educational. Always run your recipe through a liquid soap calculator, follow proper safety practices, and have any product professionally assessed before selling it.