--- title: "Skincare Glossary — School of Dermatology" description: "A comprehensive glossary of skincare and dermatology terms explained in plain English. From AHA to Zinc Oxide, understand every ingredient and concept." lang: en json-ld: | [ { "@context": "https://schema.org", "@type": "DefinedTermSet", "name": "School of Dermatology Skincare Glossary", "description": "A comprehensive glossary of dermatology and skincare terms explained in plain English.", "url": "https://schoolofdermatology.com/glossary" }, { "@context": "https://schema.org", "@type": "BreadcrumbList", "itemListElement": [ { "@type": "ListItem", "position": 1, "name": "Home", "item": "https://schoolofdermatology.com/" }, { "@type": "ListItem", "position": 2, "name": "Glossary", "item": "https://schoolofdermatology.com/glossary" } ] } ] --- [![School of Dermatology](/assets/logo-AGZDufdq.svg)](/) Articles [Skin Types](/skin-types) Tools [Glossary](/glossary) # Skincare Glossary Every skincare and dermatology term you need to know, explained in plain English. [A](#letter-A)[B](#letter-B)[C](#letter-C)[D](#letter-D)[E](#letter-E)[F](#letter-F)[G](#letter-G)[H](#letter-H)[I](#letter-I)[J](#letter-J)[K](#letter-K)[L](#letter-L)[M](#letter-M)[N](#letter-N)[O](#letter-O)[P](#letter-P)Q[R](#letter-R)[S](#letter-S)[T](#letter-T)[U](#letter-U)[V](#letter-V)[W](#letter-W)[X](#letter-X)Y[Z](#letter-Z) [Home](/)/ Glossary ## A [AHA (Alpha Hydroxy Acid)](/glossary/aha-alpha-hydroxy-acid) — Alpha hydroxy acids are a group of water-soluble acids derived from fruits, milk, and sugar cane. The most common AHAs i… [Antioxidant](/glossary/antioxidant) — Antioxidants are molecules that protect the skin from damage caused by free radicals — unstable atoms generated by UV ra… [Astringent](/glossary/astringent) — An astringent is a topical product or ingredient that causes the contraction of skin cells and tissues, temporarily tigh… [Atopic Dermatitis](/glossary/atopic-dermatitis) — Atopic dermatitis is a chronic, inflammatory skin condition and the most common form of eczema. It causes dry, itchy, re… ## B [Barrier Function](/glossary/barrier-function) — The skin's barrier function refers to the protective role of the outermost layer of the epidermis, the stratum corneum. … [BHA (Beta Hydroxy Acid)](/glossary/bha-beta-hydroxy-acid) — Beta hydroxy acid refers primarily to salicylic acid, an oil-soluble exfoliant that penetrates into pores to dissolve ex… [Broad Spectrum](/glossary/broad-spectrum) — Broad spectrum is a sunscreen classification indicating that a product protects against both UVA and UVB rays. UVB rays … ## C [Ceramides](/glossary/ceramides) — Ceramides are a family of waxy lipid molecules that occur naturally in the skin and make up about 50% of the lipids in t… [Chemical Exfoliant](/glossary/chemical-exfoliant) — A chemical exfoliant is a skincare product that uses acids or enzymes to dissolve the bonds between dead skin cells, pro… [Collagen](/glossary/collagen) — Collagen is the most abundant protein in the human body, providing structural support to the skin, bones, tendons, and l… [Comedogenic](/glossary/comedogenic) — Comedogenic describes an ingredient or product that has a tendency to clog pores and contribute to the formation of come… [Comedone](/glossary/comedone) — A comedone is a basic acne lesion formed when a hair follicle becomes clogged with dead skin cells, sebum, and sometimes… [Contact Dermatitis](/glossary/contact-dermatitis) — Contact dermatitis is a localized skin inflammation that occurs when the skin comes into direct contact with a substance… [Cystic Acne](/glossary/cystic-acne) — Cystic acne is the most severe form of acne, characterized by large, deep, painful, inflamed breakouts that form beneath… ## D [Dermatitis](/glossary/dermatitis) — Dermatitis is a general term for skin inflammation, characterized by redness, swelling, itching, and sometimes blisterin… [Dermis](/glossary/dermis) — The dermis is the thick middle layer of the skin, located between the epidermis (outer layer) and the hypodermis (subcut… [Desquamation](/glossary/desquamation) — Desquamation is the natural, ongoing process by which the outermost layer of dead skin cells (corneocytes) sheds from th… [Double Cleansing](/glossary/double-cleansing) — Double cleansing is a two-step face washing method that originated in Korean and Japanese skincare routines. The first s… ## E [Elastin](/glossary/elastin) — Elastin is a highly elastic protein found in the dermis that allows the skin to stretch and snap back to its original sh… [Emollient](/glossary/emollient) — An emollient is a type of moisturizing ingredient or product that works by filling in the gaps between skin cells with l… [Emulsifier](/glossary/emulsifier) — An emulsifier is an ingredient that allows two normally immiscible substances — typically oil and water — to mix togethe… [Enzymes](/glossary/enzymes) — In skincare, enzymes are biological proteins used as gentle exfoliating agents. They work by breaking down the keratin p… [Epidermis](/glossary/epidermis) — The epidermis is the outermost layer of the skin and serves as the body's primary physical barrier against the environme… [Exfoliation](/glossary/exfoliation) — Exfoliation is the process of removing dead skin cells from the surface of the skin to reveal fresher, smoother skin ben… ## F [Fibroblast](/glossary/fibroblast) — Fibroblasts are the primary cells in the dermis responsible for producing collagen, elastin, glycosaminoglycans (like hy… [Fitzpatrick Scale](/glossary/fitzpatrick-scale) — The Fitzpatrick Scale is a numerical classification system developed by dermatologist Thomas Fitzpatrick in 1975 that ca… [Free Radicals](/glossary/free-radicals) — Free radicals are unstable, reactive molecules with unpaired electrons that damage cells by stealing electrons from othe… ## G [Glycerin](/glossary/glycerin) — Glycerin (also called glycerol) is one of the most effective and widely used humectant ingredients in skincare. It is a … [Glycolic Acid](/glossary/glycolic-acid) — Glycolic acid is the smallest and most widely researched alpha hydroxy acid (AHA), derived from sugar cane. Its small mo… ## H [Humectant](/glossary/humectant) — A humectant is a type of moisturizing ingredient that attracts and binds water molecules from the environment and from d… [Hyaluronic Acid](/glossary/hyaluronic-acid) — Hyaluronic acid (HA) is a naturally occurring glycosaminoglycan found throughout the body's connective tissues, with the… [Hyperpigmentation](/glossary/hyperpigmentation) — Hyperpigmentation is a common skin condition where patches of skin become darker than the surrounding areas due to exces… [Hypodermis](/glossary/hypodermis) — The hypodermis, also called the subcutaneous layer or subcutis, is the deepest layer of the skin lying below the dermis.… ## I [Inflammation](/glossary/inflammation) — Inflammation is the immune system's response to injury, infection, or irritation, characterized by redness, swelling, he… [Irritant](/glossary/irritant) — An irritant is any substance that causes a non-allergic inflammatory reaction when it comes into contact with the skin. … ## J [Jojoba Oil](/glossary/jojoba-oil) — Jojoba oil is a liquid wax ester extracted from the seeds of the jojoba plant (Simmondsia chinensis), native to the sout… ## K [Keratin](/glossary/keratin) — Keratin is a tough, fibrous structural protein that is the primary component of the outermost layer of skin (stratum cor… [Keratinocyte](/glossary/keratinocyte) — Keratinocytes are the predominant cell type in the epidermis, making up approximately 90% of epidermal cells. They are p… ## L [Lactic Acid](/glossary/lactic-acid) — Lactic acid is an alpha hydroxy acid (AHA) derived from milk that serves as a gentle chemical exfoliant. It has a larger… [LED (Light Emitting Diode)](/glossary/led-light-emitting-diode) — In skincare, LED refers to light emitting diode technology used to deliver specific wavelengths of light to the skin. Di… [Lipid Barrier](/glossary/lipid-barrier) — The lipid barrier (also called the lipid matrix or lipid bilayer) is the intercellular 'mortar' between the corneocytes … ## M [Melanin](/glossary/melanin) — Melanin is the natural pigment produced by melanocytes in the basal layer of the epidermis that gives skin, hair, and ey… [Melanocyte](/glossary/melanocyte) — Melanocytes are specialized cells located in the basal layer of the epidermis that produce melanin, the pigment responsi… [Microbiome](/glossary/microbiome) — The skin microbiome refers to the vast community of microorganisms — including bacteria, fungi, viruses, and mites — tha… [Milia](/glossary/milia) — Milia are small, white or yellowish, dome-shaped bumps that appear on the skin when keratin (a protein) becomes trapped … [Moisturizer](/glossary/moisturizer) — A moisturizer is a skincare product designed to hydrate the skin and prevent water loss by combining three types of mois… ## N [Niacinamide](/glossary/niacinamide) — Niacinamide (also known as nicotinamide) is a form of vitamin B3 that has become one of the most versatile and popular a… [Non-Comedogenic](/glossary/non-comedogenic) — Non-comedogenic is a term used to describe skincare and cosmetic products that are formulated to be less likely to clog … ## O [Occlusives](/glossary/occlusives) — Occlusives are a category of moisturizing ingredients that work by forming a physical barrier on the skin's surface to p… [Oxidative Stress](/glossary/oxidative-stress) — Oxidative stress occurs when there is an imbalance between the production of free radicals (reactive oxygen species) and… ## P [Peptides](/glossary/peptides) — Peptides are short chains of amino acids (typically 2-50 amino acids long) that serve as building blocks for proteins li… [pH Balance](/glossary/ph-balance) — pH (potential of hydrogen) is a measure of acidity or alkalinity on a scale of 0 to 14, with 7 being neutral. Healthy sk… [Photobiomodulation](/glossary/photobiomodulation) — Photobiomodulation is the use of specific wavelengths of light — typically red and near-infrared — to stimulate cellular… [PIE (Post-Inflammatory Erythema)](/glossary/pie-post-inflammatory-erythema) — Post-inflammatory erythema (PIE) refers to the flat, pink to red or purple marks left on the skin after an inflammatory … [PIH (Post-Inflammatory Hyperpigmentation)](/glossary/pih-post-inflammatory-hyperpigmentation) — Post-inflammatory hyperpigmentation (PIH) is a type of hyperpigmentation that occurs as the skin heals from inflammation… [Pore](/glossary/pore) — Pores are the tiny openings on the skin's surface through which hair follicles reach the surface and through which sebum… [Propolis](/glossary/propolis) — Propolis is a natural, resinous substance produced by honeybees from tree buds, sap flows, and other botanical sources. … ## R [Red Light Therapy](/glossary/red-light-therapy) — Red light therapy uses wavelengths between 620-700 nanometers to penetrate the skin and stimulate mitochondrial energy p… [Retinoid](/glossary/retinoid) — Retinoids are a class of chemical compounds derived from vitamin A that are widely considered the gold standard in anti-… [Retinol](/glossary/retinol) — Retinol is the most popular and widely available over-the-counter form of vitamin A (retinoid) used in skincare. It is a… [Rosacea](/glossary/rosacea) — Rosacea is a chronic, inflammatory skin condition that primarily affects the central face — cheeks, nose, chin, and fore… ## S [Salicylic Acid](/glossary/salicylic-acid) — Salicylic acid is a beta hydroxy acid (BHA) derived from willow bark that is one of the most effective and widely used i… [Sebaceous Gland](/glossary/sebaceous-gland) — Sebaceous glands are small, oil-producing glands attached to hair follicles throughout the body (except on the palms and… [Sebum](/glossary/sebum) — Sebum is the waxy, oily substance produced by sebaceous glands to lubricate and waterproof the skin and hair. It is comp… [Sensitized Skin](/glossary/sensitized-skin) — Sensitized skin is a condition where the skin has become temporarily reactive, irritated, and easily aggravated due to e… [Skin Cycling](/glossary/skin-cycling) — Skin cycling is a skincare method popularized by dermatologist Dr. Whitney Bowe that involves rotating active ingredient… [SPF](/glossary/spf) — SPF stands for Sun Protection Factor, a numerical rating that indicates how much longer a sunscreen allows you to stay i… [Stratum Corneum](/glossary/stratum-corneum) — The stratum corneum is the outermost sublayer of the epidermis and the body's first physical barrier against the externa… [Sunscreen](/glossary/sunscreen) — Sunscreen is a topical product that protects the skin from the harmful effects of ultraviolet (UV) radiation, which caus… ## T [Toner](/glossary/toner) — A toner is a liquid skincare product applied after cleansing and before serums and moisturizers. Historically, toners we… [Transepidermal Water Loss (TEWL)](/glossary/transepidermal-water-loss-tewl) — Transepidermal water loss (TEWL) is the process by which water passes from the dermis through the epidermis and evaporat… [Tretinoin](/glossary/tretinoin) — Tretinoin (all-trans retinoic acid) is the most potent and well-researched prescription retinoid, available under brand … ## U [Urea](/glossary/urea) — Urea is a naturally occurring compound found in the skin as part of the natural moisturizing factor (NMF) — the collecti… [UVA](/glossary/uva) — UVA (Ultraviolet A) rays are the longest wavelength of ultraviolet radiation (320-400 nm) emitted by the sun. They accou… [UVB](/glossary/uvb) — UVB (Ultraviolet B) rays are medium-wavelength ultraviolet radiation (280-320 nm) that primarily affects the epidermis, … ## V [Vitamin C (Ascorbic Acid)](/glossary/vitamin-c-ascorbic-acid) — Vitamin C (L-ascorbic acid) is one of the most researched and effective antioxidant ingredients in skincare. It neutrali… [Vitamin E (Tocopherol)](/glossary/vitamin-e-tocopherol) — Vitamin E (tocopherol) is a fat-soluble antioxidant that occurs naturally in the skin's sebum and plays a critical role … ## W [Whiteheads](/glossary/whiteheads) — Whiteheads (closed comedones) are a type of non-inflammatory acne that appears as small, flesh-colored or white bumps on… [Witch Hazel](/glossary/witch-hazel) — Witch hazel is a plant-derived ingredient extracted from the bark and leaves of the Hamamelis virginiana shrub, native t… ## X [Xeroderma](/glossary/xeroderma) — Xeroderma is the medical term for abnormally dry skin, characterized by roughness, tightness, flaking, scaling, cracking… ## Z [Zinc (topical)](/glossary/zinc-topical) — Topical zinc refers to various zinc compounds used in skincare for their anti-inflammatory, antimicrobial, wound-healing… [Zinc Oxide](/glossary/zinc-oxide) — Zinc oxide is a mineral (inorganic) sunscreen ingredient that provides broad-spectrum protection against both UVA and UV… Skincare Updates Weekly articles in your inbox. 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