The cosmetic chemistry terms you need to read an INCI list with confidence.
The slightly acidic film on the skin's surface (pH 4.5–5.5) formed by sebum, sweat, and skin microbiome activity. It protects against pathogens and maintains barrier integrity.
A class of water-soluble exfoliating acids including glycolic acid, lactic acid, and mandelic acid. Effective at pH 3.0–4.0. Increase cell turnover and improve skin texture.
Containing no water. Anhydrous formulations (balms, oils, waxes) do not require preservation against microbial growth but may require antioxidants to prevent oxidation.
The skin's ability to prevent water loss (TEWL) and resist penetration of irritants, allergens, and pathogens. Primarily maintained by the stratum corneum's lipid matrix including ceramides, cholesterol, and fatty acids.
Oil-soluble exfoliating acid, primarily salicylic acid. Penetrates into the follicle and is effective for acne-prone skin. Active at pH 3.0–4.0.
An ingredient that binds to metal ions (particularly calcium and magnesium) in formulations, preventing them from destabilising the product or reducing preservative efficacy. Common examples: Disodium EDTA, Phytic Acid.
Tending to block pores and potentially cause comedones (blackheads and whiteheads). Comedogenicity is rated on a 0–5 scale, though the scale's predictive validity for human skin is limited.
An ingredient that softens and smooths the skin by filling in gaps between skin cells with lipids. Emollients improve skin texture and reduce water loss without forming a complete occlusive barrier.
An ingredient that stabilises emulsions by sitting at the interface between oil and water phases, preventing separation. Characterised by HLB value.
A mixture of two immiscible liquids (typically oil and water) stabilised by an emulsifier. Can be oil-in-water (O/W) or water-in-oil (W/O). Most moisturisers and creams are O/W emulsions.
The un-ionised, active form of an acid. For AHAs and BHAs, only the free acid form penetrates the skin and delivers exfoliation. The proportion of free acid is determined by the product's pH.
A numerical scale (0–20) that describes an emulsifier's relative affinity for water versus oil. Emulsifiers with HLB 8–18 are suitable for O/W emulsions; those with HLB 3–6 for W/O emulsions.
An ingredient that attracts and retains water molecules from the environment and deeper skin layers into the stratum corneum. Examples: glycerin, hyaluronic acid, urea, panthenol.
International Nomenclature of Cosmetic Ingredients. The standardised naming system for cosmetic ingredients, developed by the Personal Care Products Council and adopted globally. All cosmetic products must list ingredients using INCI names.
The full ingredient declaration on a cosmetic product, using INCI names listed in descending order of concentration (above 1%). The most reliable source of information about what a product contains.
An ingredient that breaks down the protein bonds holding dead skin cells together, promoting exfoliation. Examples: urea (at high concentrations), salicylic acid, AHAs.
The mass of a molecule, measured in Daltons (Da) or kiloDaltons (kDa). In skincare, molecular weight determines skin penetration depth. Lower molecular weight molecules penetrate more deeply.
An ingredient that forms a physical barrier on the skin surface, preventing transepidermal water loss (TEWL). Examples: petrolatum, dimethicone, beeswax, lanolin.
A scale from 0–14 measuring hydrogen ion concentration. Acidic solutions have pH below 7; alkaline above 7. Skin's natural pH is 4.5–5.5. Many cosmetic actives have narrow pH windows for efficacy.
An ingredient that prevents microbial growth (bacteria, yeast, mould) in cosmetic formulations. Required in all water-containing products. Common examples: phenoxyethanol, parabens, sodium benzoate.
The outermost layer of the epidermis, composed of dead, flattened keratinocytes (corneocytes) embedded in a lipid matrix. The primary barrier against water loss and external penetration.
The passive diffusion of water through the skin to the environment. Elevated TEWL indicates a compromised skin barrier. Occlusives reduce TEWL by forming a physical barrier.