The words we use

The list of restricted substances in the EU Cosmetics Regulation (EC) No 1223/2009 — ingredients permitted only under stated limits.

The EU's positive list of permitted UV filters and their maximum concentrations.

Cosmetic Ingredient Review. A US industry-funded, independent expert panel that assesses ingredient safety.

Tending to cause comedones (blocked pores). Historical rabbit-ear ratings translate poorly to finished products on human skin.

Health Canada's list of prohibited and restricted cosmetic ingredients.

The fraction of an acid that is un-ionised at a given pH — the part that actually penetrates and exfoliates. Depends on pH and pKa, not just percentage.

Generally Recognised As Safe and Effective. The FDA category for OTC drug ingredients, including sunscreen filters, that may be marketed without pre-approval.

International Nomenclature of Cosmetic Ingredients — the standardised names used on ingredient lists worldwide. The Index shows INCI names in monospace.

A product intended to remain on skin (serums, creams, sunscreens). Regulatory limits are often stricter than for rinse-off.

Melasma Area and Severity Index. The standard outcome measure in melasma trials.

Symmetrical brown patches, usually on the face, driven by hormones and UV. Measured in trials with the MASI score.

A material with particles in the 1–100 nm range. In the EU, nano ingredients must be labelled '(nano)' and assessed separately.

Randomised controlled trial. Participants are randomly assigned to treatment or control; the design that most reliably isolates an ingredient's effect.

A way of expressing retinyl esters as the amount of retinol they yield. EU limits are stated in retinol equivalents.

A product removed shortly after application (cleansers, masks). Lower exposure, so often higher permitted concentrations.

Scientific Committee on Consumer Safety. The EU body whose opinions underpin most cosmetic ingredient restrictions.

A trial design where one side of the face receives the active and the other the vehicle, controlling for individual variation.

The outermost layer of the epidermis: flattened dead cells (corneocytes) in a lipid matrix. Where most cosmetics act.

Transepidermal water loss. The rate water evaporates through the stratum corneum; a standard proxy for barrier function.

The base formulation without the active ingredient. A vehicle-controlled trial compares active-in-base against base alone.