Glossary.

The vocabulary of cosmetic formulation, in plain language.

Active ingredient: An ingredient included in a formula specifically to produce the product's intended effect, as distinct from ingredients that build or stabilise the base.
Anhydrous: Containing no added water. Balms, oils, and many sticks are anhydrous products.
Antioxidant: An ingredient used to slow oxidation, either to protect the formula itself or as part of its intended effect on the application surface.
Chelating agent: An ingredient that binds trace metal ions in a formula, helping preservation, colour stability, and cleansing performance.
Color additive: A material used to impart colour. Colour additives are regulated separately from other cosmetic ingredients in many markets.
Conditioning agent: An ingredient that improves the feel, smoothness, or manageability of skin or hair after use.
Emollient: An ingredient that softens and smooths the surface, typically by filling gaps between surface cells and improving slip.
Emulsifier: An ingredient that allows oil and water to be combined into one stable product by reducing tension between the two phases.
Emulsion: A stable mixture of two materials that do not normally mix — most commonly oil dispersed in water, or water dispersed in oil.
Humectant: An ingredient used to attract or retain water within a cosmetic system or at the application surface.
INCI: International Nomenclature of Cosmetic Ingredients — the standardised naming system used on cosmetic ingredient lists so the same material has the same name worldwide.
Occlusive: An ingredient that forms a layer on the surface which slows the rate at which water evaporates from it.
Peptide: A short chain of amino acids. Peptides are used in cosmetics for a range of intended surface effects and vary widely in structure and stability.
Preservative: An ingredient system included to prevent microbial growth in a product over its shelf life and during consumer use.
Rheology: The study of how a material flows and deforms — what makes a gel hold its shape or a lotion pour.
Serum: A lightweight, usually thin product designed to deliver a concentrated set of ingredients with minimal occlusive base.
Skin barrier: The outermost layers of skin and their lipid structure, which limit water loss and act as the skin's primary physical defence.
Surfactant: A surface-active ingredient with both water-loving and oil-loving parts, used for cleansing, foaming, solubilising, or emulsifying.
Viscosity: A measure of a liquid's resistance to flow. Higher viscosity means thicker and slower-moving.
Water activity: A measure of how much water in a formula is available to support microbial growth, which influences preservation strategy.