Skincare Glossary: The Words, in the Order You Meet Them

This skincare glossary is built for looking things up rather than reading through. Each entry gives the definition in one sentence and then points at the page that works it out properly, with the sources attached there rather than repeated here.

The grouping is by where the word turns up, since that is how skincare terms explained anywhere else usually go wrong: an alphabetical list puts a labeling rule next to a skin condition as though they were the same kind of thing.

Where a term is a cosmetics word rather than a clinical one, the entry says so. That distinction is not decoration. It tells you whether there is a standard behind the word or only an industry habit.

On the label

The 1 percent line. The threshold below which ingredients can be listed in any order, so position stops carrying information about how much is present. See how to read a skincare ingredient list.

Fragrance. A single label word covering a mixture that does not have to be broken out ingredient by ingredient. See how to read a skincare ingredient list.

"May contain." The phrasing that lets one label cover several shade variants, listing the colorants any of them might include. See how to read a skincare ingredient list.

Hypoallergenic. A marketing word with no required definition behind it, which the FDA states plainly on its own page about the term. See skincare label claims.

Non-comedogenic. A claim that a product is unlikely to clog pores, made without a standardized test anyone is obliged to use. See skincare label claims.

Dermatologist tested. A claim that some testing involving a dermatologist happened, which says nothing about what was tested or what the result was. See skincare label claims.

Clinically proven. A claim that a study exists, with no requirement to say what the study compared, measured, or found. See skincare label claims and, for reading the study itself, reading clinical claims.

Cosmeceutical. An industry coinage for products positioned between cosmetics and drugs, with no regulatory status of its own. Cosmetics term, not a clinical one. See skincare label claims.

Drug Facts panel. The panel that appears when a product is regulated as an over-the-counter drug rather than a cosmetic, which is why its active ingredient and concentration are printed. See salicylic acid.

In the formula

Humectant. An ingredient that attracts and holds water in the outer layer of skin. See skincare ingredient types.

Occlusive. An ingredient that forms a hydrophobic layer on the surface, slowing water leaving the skin. See skincare ingredient types.

Emollient. An oily ingredient that softens and smooths by filling gaps in the outermost layer. See skincare ingredient types.

Actives. The ingredients meant to change something rather than to condition the surface or keep the product stable. See skincare ingredient types.

Preservatives. The ingredients that stop a water-containing product from growing bacteria and fungi in the jar. See skincare ingredient types.

Vehicle. Everything in a formula apart from the active, which in a trial is what the control group receives. See reading clinical claims.

Formulation pH. The acidity of the finished product, which decides how an acid behaves at any given concentration and is almost never printed. See skin pH.

Concentration limit. The upper bound a safety assessment attaches to an ingredient, usually alongside conditions rather than on its own. See glycolic acid percentage.

Retinoid. The umbrella term for vitamin A derivatives, which spans cosmetic ingredients, an over-the-counter drug and prescription molecules. See retinol versus retinoid and, for how the forms rank, the retinoid strength ladder.

Vitamin C forms. L-ascorbic acid is the active form; the derivatives trade its instability and sting for a thinner evidence base on delivery. See vitamin C forms compared.

On your skin

Comedone. A clogged follicle, open at the surface as a blackhead or sealed as a closed comedone. See closed comedones.

Sebaceous filament. The name commonly given to the gray dots on the nose, treated as a normal structure rather than a clog. Popular term whose boundary with a blackhead is less settled than the advice suggests. See sebaceous filaments versus blackheads.

Milia. Small, hard, white bumps under intact skin, described in the clinical literature as benign keratinizing lesions rather than trapped debris. See milia under the eyes.

Purging. The idea that an active temporarily worsens skin by bringing existing congestion up faster, a widely repeated account with thin trial evidence behind it. See purging versus breakout.

Barrier damage. Consumer language for what the clinical literature usually calls irritant contact dermatitis. Consumer term with a clinical counterpart. See damaged skin barrier.

Dehydrated skin. Skin short of water rather than oil, though the clinical definitions of dry skin do not split as cleanly along that line as the popular version claims. See dehydrated skin versus dry skin.

Postinflammatory hyperpigmentation (PIH). The brown or gray-brown mark left after inflammation, from melanin deposited during healing. See dark spots after acne.

Malassezia folliculitis. The yeast-driven eruption usually called fungal acne, which looks like acne and responds to different treatment. See fungal acne versus regular acne.

Textured skin. A description of how skin feels rather than a diagnosis, covering at least five different causes. Descriptive term, not a condition. See textured skin.

In the evidence, and at the clinic

Evidence grades. The four-step scale used across this site, from repeated independent human trials down to cell-culture work only. See how we rate skincare evidence.

Vehicle-controlled. A trial design where the control group gets the formula minus the active, which is the only kind of control a topical trial can run. See reading clinical claims.

Individual typology angle (ITA). A measured, instrument-based number for skin depth, calculated from lightness and the yellow-blue axis. See how skin tone is measured.

Undertone. Where skin sits on the hue axes underneath its depth. Cosmetics term, not a clinical one, with no standard behind it. See why undertone tests fail.

Olive. A lean toward green on the red-green axis, which the warm-cool vocabulary has no coordinate for. Cosmetics term, unstandardized. See olive undertone.

FAAD. The designation indicating a physician is a Fellow of the American Academy of Dermatology, used when checking who you are booking with. See how to prepare for a dermatologist appointment.

Teledermatology. Dermatology delivered remotely, by photographs or video, with limits that depend on what needs to be examined. See teledermatology platforms compared and online dermatology versus in person.

Terms not included, and why

Three kinds of skincare vocabulary are missing from this list on purpose.

Words this site has not worked through yet. A term earns an entry once there is a page behind it that shows the sources. Anything else would be a definition with nothing to check it against.

Brand-coined ingredient names. Trademarked complexes and proprietary blends are marketing vocabulary, and defining them here would treat them as a shared standard when each belongs to one company.

Prescription drug terminology. This site covers care and product choice rather than disease, so dosing and prescribing vocabulary stays with the clinicians who use it.

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Skincare ingredient terms are not hard because the ideas are difficult. They are hard because the same word carries a legal meaning on one label, a chemical meaning in one formula, and a marketing meaning on the front of the box. Knowing which of the three you are looking at is most of the work. The figures behind those words are collected the same way in skincare numbers, each quoted from its source with the condition it depends on.