Beauty Glossary

Plain-English definitions of skincare ingredients, makeup techniques, hair care terms, and beauty industry jargon. Use the alphabet below to jump to any section.

How to use this glossary

Beauty terms explained simply

Every term is defined in plain English with practical context — what it does, who it's for, and how to use it. Click linked terms to jump to related guides. Use the sticky alphabet bar to find any letter quickly. Updated monthly with new reader-requested terms.

Niacinamide
Vitamin B3 used in skincare to strengthen the skin barrier, reduce redness, and minimize pore appearance. Suits all skin types.
Retinol
An over-the-counter vitamin A derivative used for anti-aging, acne, and texture. Causes initial peeling; requires SPF.
Broad-Spectrum SPF
Sunscreen that blocks both UVA (aging) and UVB (burning) rays. Look for "broad-spectrum" on the label, not just SPF.
Hyaluronic Acid
A humectant that holds up to 1,000× its weight in water, plumping and hydrating skin's surface.
Salicylic Acid
The main BHA in skincare. Oil-soluble, penetrates pores, treats blackheads and oily skin. Effective at 0.5–2%.
Ceramide
A natural skin lipid. Topical ceramides repair compromised barriers and reduce sensitivity.

A

AHA (Alpha Hydroxy Acids)
Water-soluble exfoliating acids derived from fruits, milk, or sugar. Common types include glycolic acid, lactic acid, and mandelic acid. AHAs work on the skin's surface to remove dead cells, brighten tone, and improve texture. Best for dry, sun-damaged, or aging skin. See AHA vs BHA comparison.
Acrylic Nails
A nail enhancement made from a liquid monomer and powder polymer that hardens into a durable overlay. Lasts 3–4 weeks. More damaging to natural nails than gel or BIAB. Read our manicure comparison.
Antioxidant
An ingredient that neutralizes free radicals (unstable molecules from UV, pollution, and stress) that damage skin cells. Common skincare antioxidants: vitamin C, vitamin E, ferulic acid, niacinamide, resveratrol.
Azelaic Acid
A gentle multi-tasking ingredient that reduces redness, treats acne, fades hyperpigmentation, and improves skin texture. Suitable for sensitive skin and rosacea. Available over-the-counter at 10% and prescription at 15–20%.

B

BHA (Beta Hydroxy Acid)
An oil-soluble exfoliating acid — almost exclusively salicylic acid in skincare. Penetrates pores to dissolve oil and dead skin, making it ideal for oily, acne-prone, and combination skin.
BIAB (Builder In A Bottle)
A soft gel applied to natural nails to strengthen and protect them, while still allowing length growth. Considered the gentlest of long-wear manicures. Lasts 3–4 weeks. Compare BIAB to gel and acrylic.
Broad-Spectrum SPF
Sunscreen that protects against both UVA (aging) and UVB (burning) rays. Always look for "broad-spectrum" on the label — SPF alone only refers to UVB protection.

C

Ceramide
A naturally occurring lipid that forms part of the skin barrier. Topical ceramides help repair compromised barriers, reduce sensitivity, and lock in moisture. Essential for dry, eczema-prone, and mature skin.
Comedogenic
An ingredient or product likely to clog pores and cause comedones (blackheads/whiteheads). "Non-comedogenic" labeling is unregulated, but generally indicates the formula avoids known pore-clogging ingredients.
Curly Girl Method (CGM)
A hair-care approach for curly and wavy hair that avoids sulfates, silicones, and heat to encourage natural curl pattern. Popularized by Lorraine Massey's book. Read our CGM guide.

D

Dermatologist-Tested
Means a dermatologist was involved in product testing — but doesn't specify what was tested or whether the dermatologist endorsed the product. Different from "dermatologist-recommended," which is also unregulated marketing language.
Double Cleansing
A two-step cleansing routine: first an oil-based cleanser to remove sunscreen, makeup, and sebum, then a water-based cleanser to remove sweat and dirt. Particularly useful at the end of the day.

E

Eau de Parfum (EDP)
Fragrance with 15–20% perfume oil concentration. Lasts 6–8 hours. Stronger and longer-wearing than eau de toilette but less concentrated than parfum/extrait.
Eau de Toilette (EDT)
Fragrance with 5–15% perfume oil concentration. Lasts 3–5 hours. Lighter and fresher than eau de parfum, often used for daytime or summer.
Emollient
An ingredient that softens and smooths skin by filling gaps between skin cells. Examples: squalane, shea butter, jojoba oil, fatty alcohols.
Exfoliation
The process of removing dead skin cells from the surface. Two main types: physical (scrubs, brushes) and chemical (AHAs, BHAs, enzymes). Chemical is generally gentler and more effective.

F

Fitzpatrick Skin Type
A six-point scale (I–VI) classifying skin by how it responds to UV exposure. Used by dermatologists to predict skin cancer risk and guide treatment recommendations.
Fragrance-Free
No added fragrance, masking ingredients, or essential oils used for scent. Different from "unscented," which may contain masking fragrances. Recommended for sensitive skin.

G

Gel Polish
A thin nail polish cured under UV/LED light, lasting 2–3 weeks. Less damaging than acrylic but more than BIAB. Requires soak-off removal with acetone.
Glycolic Acid
The smallest AHA molecule, derived from sugar cane. Most penetrating of the AHAs and most effective for anti-aging, but also most irritating. Start at 5–8% concentrations.

H

Humectant
An ingredient that draws water into the skin from deeper layers and the air. Examples: hyaluronic acid, glycerin, urea. Most effective when sealed with an occlusive moisturizer.
Hyaluronic Acid (HA)
A humectant naturally found in skin that holds up to 1,000 times its weight in water. Topical HA plumps and hydrates the skin's surface. Look for products with multiple molecular weights for deeper hydration.
Hyperpigmentation
Dark patches caused by excess melanin production from sun damage, hormones, inflammation, or injury. Treatable with vitamin C, niacinamide, retinoids, azelaic acid, tranexamic acid, and SPF.

I

INCI
International Nomenclature of Cosmetic Ingredients — the standardized scientific naming system used on product ingredient labels worldwide. Learning to read INCI helps you spot actives and irritants.

K

Keratin
The structural protein that makes up hair, nails, and the outer layer of skin. Keratin treatments smooth hair by depositing protein and sealing it with heat — effects last 2–4 months.

L

Lactic Acid
A gentle AHA derived from milk. More hydrating than glycolic acid and better tolerated by dry or sensitive skin. Effective at 5–10% concentrations.

M

Microbiome (Skin)
The community of bacteria, fungi, and microorganisms living on healthy skin. A balanced microbiome supports the skin barrier; harsh products can disrupt it. Look for prebiotic and postbiotic skincare to support balance.
Mineral Sunscreen
Sunscreen using zinc oxide and/or titanium dioxide, which sit on the skin's surface and physically block UV rays. Often called "physical sunscreen." Better tolerated by sensitive and reactive skin than chemical filters.

N

Niacinamide (Vitamin B3)
A multitasking ingredient that strengthens the skin barrier, reduces redness, controls oil, minimizes the appearance of pores, and fades hyperpigmentation. Effective at 2–10%. Tolerated by virtually all skin types. Compare niacinamide to retinol.
Non-Comedogenic
Marketing term indicating a formula is unlikely to clog pores. Unregulated, but typically excludes known comedogenic ingredients. Useful starting filter for acne-prone skin, but individual reactions vary.

O

Occlusive
An ingredient that forms a protective barrier on the skin to prevent water loss. Examples: petrolatum, lanolin, mineral oil, beeswax. Essential for very dry skin and "slugging" routines.

P

Patch Test
Applying a small amount of a new product to a discreet area (behind the ear or inner wrist) for 24–48 hours before full use, to check for allergic or irritant reactions.
pH (in skincare)
The acidity of a product. Healthy skin sits at pH 4.5–5.5. Cleansers and acids work at specific pH ranges to be effective. Soap (pH 9–10) disrupts skin barrier; gentle cleansers (pH 5.5) preserve it.
Pomade
A heavy hair styling product that adds shine and hold without stiffness. Water-based pomades wash out easily; oil-based versions provide stronger hold but need clarifying shampoo.

R

Retinoid
A category of vitamin A derivatives — including retinol, retinaldehyde, retinyl esters, and prescription tretinoin. The gold standard for anti-aging, acne, and skin texture.
Retinol
An over-the-counter retinoid that converts to retinoic acid in skin. Reduces wrinkles, improves texture, treats acne, and fades pigmentation. Start 1–2 nights/week and build tolerance gradually. See niacinamide vs retinol guide.

S

Salicylic Acid
The main BHA in skincare. Oil-soluble, so it penetrates pores to clear oil and dead skin. Best for blackheads, whiteheads, and oily skin. Effective at 0.5–2%.
Slugging
Applying a thick occlusive (typically petrolatum) as the last skincare step at night to lock in hydration. Best for dry skin types and damaged barriers; not recommended for acne-prone skin.
SPF (Sun Protection Factor)
A measure of UVB protection. SPF 30 blocks ~97% of UVB; SPF 50 blocks ~98%. The numbers are based on lab testing; real-world protection depends on application thickness and reapplication.
Squalane
A stable, plant-derived (or olive-derived) lipid that mimics skin's natural sebum. Lightweight, non-comedogenic, and suitable for all skin types. Excellent emollient.

T

Toner
A water-based product applied after cleansing. Modern toners hydrate, balance pH, and deliver actives. The harsh, alcohol-based "astringent toners" of the past are largely outdated.
Tretinoin
The prescription-strength retinoid; the most studied and effective form of vitamin A in skincare. Faster results than retinol but stronger initial side effects (peeling, redness).
Trichologist
A certified specialist in hair and scalp health. Not a medical doctor — for medical hair-loss conditions, see a dermatologist. For everyday hair concerns, a trichologist offers expert guidance.

U

UVA
Ultraviolet A rays — long-wave radiation that penetrates deep into the dermis, causing premature aging, wrinkles, and pigmentation. Present year-round, even through windows.
UVB
Ultraviolet B rays — shorter-wave radiation that causes sunburn and most skin cancers. Strongest in summer and at high altitudes.

V

Vitamin C (L-Ascorbic Acid)
The most studied form of topical vitamin C. A potent antioxidant that brightens skin, fades pigmentation, and boosts collagen. Effective at 10–20%; unstable and oxidizes when exposed to light/air. See our vitamin C guide.

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