Basic guide to formulating homemade cosmetics safely

Making cosmetics at home can be beautiful, useful and very creative, but it is worth working methodically. This guide summarises the basics for reducing mistakes, preventing contamination and understanding why a natural formula also needs care.

The most important point: when making a cosmetic, the greatest risk is not usually that it turns out runny, unattractive or low in foam. The most serious risk is contaminating it with microorganisms and continuing to use it without realising.

Before you start Contamination Disinfection Manufacturing Preservation Common mistakes When to discard a formula Glossary

Before you start

Read the whole recipe before weighing anything. Many formulas fail because people start enthusiastically without knowing when to add each ingredient, whether to measure pH or whether to leave it to stand.

Prepare a clean, dry and clear work surface.
Weigh all ingredients before mixing.
Have a spatula, beaker, scales and pH strips or a pH meter ready when the recipe calls for them.
Do not improvise substitutions if you do not know the function of each ingredient.
Always label the product with its name, date and any changes you have made.

A simple rule: if you change an important ingredient, you are no longer making the same recipe. You are making a different formula that needs its own checks.

The greatest risk: contamination

A cosmetic can become contaminated with bacteria, fungi or yeasts. Sometimes this is visible, but often it is not. It may smell unusual, change colour, separate, produce gas or simply look normal while being unsuitable for use.

The risk increases in formulas containing water: creams, gels, shampoos, toners, micellar waters, shower gels, water-based masks or any product to which hydrolats, infusions, aloe, aqueous extracts or water are added.

Products containing water

Need a suitable preservative, unless prepared for immediate use under very limited conditions.
Need clean packaging, preferably packaging that limits contact with fingers and water.
Should not be kept in the shower if water can enter the container.

Water-free products

A body oil, anhydrous balm or whipped butter usually has a lower microbiological risk as long as no water gets in. However, it can oxidise, turn rancid or become contaminated if touched with wet hands or used in dirty surroundings.

Cleaning and disinfecting utensils and containers

Cleaning and disinfecting are different. First remove visible dirt; then reduce the microbial load.

1. Wash

Wash beakers, spatulas and containers with hot water and detergent. Rinse thoroughly so that no residue remains.

2. Dry

Leave them to dry on clean paper or a freshly washed cloth. Do not use an old or damp tea towel.

3. Disinfect

Spray suitable alcohol onto the clean surface or use a disinfection method compatible with the material.

4. Do not touch the inside

Once the container is clean, do not put your fingers inside or place the lid on the table with its inner surface facing down.

Glass containers may tolerate more intensive methods than some plastics. Not all containers withstand heat, alcohol or certain disinfectants. If the material deforms, cracks or develops an unusual smell, do not use it.

Good practices during manufacturing

Work with good ventilation, especially when using alcohol, essential oils, fine powders, fragrances or powdered surfactants.
Do not formulate while cooking, eating or cleaning with strong household products.
Avoid dust, dirty draughts and surfaces with food residue.
Tie your hair back and wash your hands before starting.
Wear gloves when handling acids, bases, preservatives, essential oils, colourants or concentrated surfactants.
Wear a mask when handling fine powders that could be inhaled.
Do not use kitchen spoons that will later be used for food without cleaning them properly.

Weighing and quantities

Formulate in grams whenever possible. This is more accurate than measuring in spoonfuls or drops. Drops vary with the dropper, viscosity and temperature.

pH

pH matters in water-based products for skin or hair. A preservative may stop working effectively outside its range. An unsuitable pH may also cause irritation or affect the formula’s stability.

Preservatives

Not every preservative is suitable for every formula. Check the dose, compatible pH, solubility, product type and phase of incorporation. Replacing one preservative with another is not always a straightforward substitution.

Natural cosmetics: shelf life and practical limits

Natural does not mean everlasting or automatically safe. A natural formula can become contaminated, oxidise or spoil if stored badly or used unhygienically.

Keep cosmetics away from heat, direct sunlight and excessive humidity.
Close the container securely after each use.
Avoid getting water into the product.
Prefer airless, pump or dispensing containers when the formula contains water.
If you use a jar, use a clean, dry spatula.
Do not share products that touch mucous membranes or delicate areas.

Actual shelf life depends on the formula, preservative, packaging, manufacturing hygiene, storage temperature and subsequent use. A well-formulated cream may spoil early if touched with wet fingers every day.

Common mistakes

Adding tap water to a finished formula.
Preparing infusions and storing them as though they were preserved hydrolats.
Using essential oils by eye.
Not measuring pH in formulas that require it.
Changing preservatives without checking the pH range and dose.
Putting fingers into jars of water-based cream.
Using unwashed containers because they look new.
Believing that a product is perfectly fine if it does not smell bad.
Heating sensitive ingredients unnecessarily.
Selling a homemade formula without the applicable assessment, documentation and legal requirements.

When to discard a formula

When there is serious doubt, the prudent choice is not to use it. A formula should be discarded if any of these signs appear:

An unusual, sour or fermented smell, or one that differs from the original.
Visible mould, unusual spots or filaments.
Gas, swelling of the container or pressure when opening.
A pronounced colour change without explanation.
Separation that was not present and was not expected.
Itching, stinging or an unexpected reaction when trying it.
Dirty water entering the product, a fall onto the floor or questionable handling.

Responsible use test

Before using a new formula regularly, try a small amount on a small area and observe. If irritation, redness, itching or discomfort occurs, rinse it off and stop using it.

If you want to sell cosmetics

An indicative homemade recipe is not the same as a product ready for sale. Selling cosmetics in the European Union involves specific obligations concerning safety, documentation, assessment, notification, labelling and manufacturing. This guide helps you formulate more carefully, but does not replace professional assessment or the necessary tests.

Glossary and quick questions

We have prepared a simple glossary of the most common cosmetic formulation terms: phases, pH, active matter, solubility, surfactants, emulsifiers, preservatives and stability.

View the homemade cosmetic formulation glossary

Useful official reading

Educational content aimed at home formulation. Published recipes are starting points and must be tested and validated before regular use or sale.