Water phase: the part of the formula made up of water or ingredients that mix with water, such as hydrolats, aloe, glycerine, certain extracts or water-soluble actives.

Oil phase: the part made up of oils, butters, waxes, esters, squalane, oil-soluble emollients and actives that dissolve in oil.

Final phase: the phase added at the end, usually when the formula is cooler. It often includes preservatives, perfumes, essential oils or heat-sensitive actives.

Anhydrous formula: a water-free formula. Examples include facial oil, balm, body butter or oil-based perfume. It has a lower microbiological risk if no water enters it, but can oxidise.

Emulsion: a stable mixture of water and oil made with the help of an emulsifier. A cream or body lotion is usually an emulsion.

Gel: a formula with a thicker texture thanks to a gelling agent such as xanthan gum, carbomer, alginate or other polymers.

Biphasic: a product with two visible layers, usually one water-based and the other oil-based. It is shaken before use and is not intended to remain permanently emulsified.

Percentage (%): the clearest way to express a formula. If a recipe contains 3% of an ingredient in 100 g, that is 3 g. In 1000 g, it is 30 g.

q.s. or quantity required: add only as much as needed to achieve an objective, such as adjusting pH or bringing a formula up to 100%.

pH: a measure of acidity or alkalinity. In cosmetics, it affects tolerability, stability and the effectiveness of certain preservatives or actives.

pH range: a range within which a formula should be kept. Not all preservatives, actives or surfactants work well at every pH.

Active matter: the genuinely active part of a raw material. This is crucial for surfactants: two products may look similar but have different actual concentrations.

Recommended dose: the usual use range for an ingredient. It does not mean that you should always use the maximum dose.

Viscosity: resistance to flow. A product may be liquid, a fluid gel, a light cream or very thick, depending on its viscosity.

Water-soluble: dissolves in water or a water phase. Usually added to the water phase or final water phase.

Oil-soluble: dissolves in oil or an oil phase. Usually added to oils or incorporated into emulsions through the oil phase or final oil phase.

Dispersible: does not dissolve completely but can be distributed through the formula by stirring. It may require suspension, gelling or constant mixing.

Solubiliser: an ingredient that helps incorporate small amounts of lipophilic substances, such as perfume or essential oil, into a water-based formula.

Humectant: helps retain water or improve the feeling of hydration. Common examples include glycerine, propanediol and panthenol.

Emollient: provides softness, slip and comfort. Examples include vegetable oils, esters, squalane and coco-caprylate/caprate.

Occlusive: forms a film that reduces water loss. It can be useful in balms, ointments or highly protective creams.

Cosmetic active: an ingredient used for a specific cosmetic benefit, such as improving hydration, radiance, the appearance of firmness or comfort.

Preservative: an ingredient that helps protect a formula against microbial growth. It is particularly important in formulas containing water.

Antioxidant: helps delay oxidation of oils or sensitive ingredients. It does not replace an antimicrobial preservative.

Chelating agent: an ingredient that helps bind metals present in water or raw materials. It may improve stability and support preservation.

Surfactant: an ingredient that helps cleanse, create foam, disperse grease or mix phases that would not normally mix.

Anionic surfactant: usually provides cleansing and foam. It may be more or less mild depending on its structure and the complete formula.

Non-ionic surfactant: usually has good compatibility and a mild profile. Some are used as cleansers, co-surfactants or solubilisers.

Amphoteric surfactant: may help make the surfactant system milder and improve foam or tolerability. Coco betaine is a common example.

Cationic surfactant: has a positive charge. It is used more often in hair conditioners than in shower gels. It is not always compatible with anionic surfactants.

Primary surfactant: mainly responsible for cleansing in a formula.

Co-surfactant: accompanies the primary surfactant to improve foam, viscosity, mildness, rinsing or stability.

Total active matter: an indicative sum of the active portion of a formula’s surfactants. It is important when comparing actual mildness and detergency.

Emulsifier: an ingredient that allows water and oil to combine in a stable emulsion.

Co-emulsifier: an ingredient that supports the main emulsifier, usually by improving texture, body or stability.

HLB: an indicative value that helps you choose emulsifiers according to the oil phase. It is useful but does not replace stability testing.

Stability: a formula’s ability to remain acceptable over time: without separating or unusual changes in smell or colour, while maintaining texture and safety.

Syneresis: loss or release of liquid from a gel or emulsion. It may indicate instability, excess electrolytes or insufficient gelling.

Opalescent: a slightly milky or pearlescent appearance. It is not always a problem; it depends on the intended formula.

GMP or good manufacturing practices: a set of working habits for orderly, clean and reproducible manufacturing, reducing errors and contamination.

Homemade batch: a number or code identifying when a formula was made and which ingredients were used. It can be as simple as a date and version.

Traceability: being able to identify which raw materials, quantities and changes were used in a preparation.

PAO: period after opening. Indicates how long a cosmetic can be used after opening if it is stored and used correctly.

Challenge test: a professional test to check the effectiveness of the preservation system against microorganisms. Looking at, smelling or keeping the cream for a few days is not a substitute.

Home patch test: an indicative tolerance test on a small area. It may detect obvious discomfort but does not demonstrate complete safety or replace professional assessment.

IFRA: a reference used to assess use limits for fragrances and essential oils by category. It is particularly important in fragranced products.

Cosmetic allergens: substances that must be declared under certain conditions according to applicable regulations. An essential oil containing declarable allergens is not necessarily impure.