The Acne Glossary: Every Term You'll Encounter, Explained Simply

Skincare has a vocabulary problem. You read an article about acne and suddenly you're neck-deep in terms like "comedolytic" and "sebaceous hyperplasia" and "post-inflammatory erythema," and the article assumes you know what all of that means. Product labels are worse. Half the words on a bottle of moisturizer might as well be in Latin (some of them literally are).

This glossary exists so you can look things up quickly and understand what people are talking about when they discuss acne. I've kept each definition short and in plain language. Where a term connects to one of our other articles, I've noted that so you can read more if you want to.

A-C

Acne vulgaris. The medical term for common acne. "Vulgaris" means "common" in Latin, not "vulgar." It covers everything from blackheads and whiteheads to cystic lesions.

Acne mechanica. Acne caused by friction, pressure, or heat against the skin. Common from helmets, chin straps, backpack straps, and face masks (maskne). Different from regular acne because the trigger is physical rather than hormonal.

Active ingredient. The ingredient in a product that actually does the advertised job. In an acne wash with 2% salicylic acid, salicylic acid is the active ingredient. Everything else (water, surfactants, fragrance) is inactive.

Adapalene. A retinoid available over the counter as Differin (0.1% gel). It normalizes skin cell turnover and reduces inflammation. One of the most effective and accessible acne treatments for teens. Takes 8-12 weeks to see full results.

AHA (alpha hydroxy acid). A family of chemical exfoliants that work on the skin surface. Glycolic acid and lactic acid are the most common. AHAs dissolve the bonds between dead skin cells, helping them shed. Better for surface texture and dry skin than for deep acne. Can increase sun sensitivity.

Androgen. A category of hormones including testosterone and DHT (see below). Androgens stimulate oil production in the skin. The surge of androgens during puberty is the main reason acne starts in the teen years.

Antibacterial. Something that kills or inhibits bacteria. Benzoyl peroxide is antibacterial. Salicylic acid is not (it's keratolytic). The distinction matters because different acne treatments work through different mechanisms.

Azelaic acid. A naturally occurring acid with anti-inflammatory, antibacterial, and mild exfoliating properties. Available in prescription strengths (15-20%) and over the counter (usually 10%). Particularly good for PIH (dark marks) and rosacea-type acne. Gentler than retinoids for many people.

Benzoyl peroxide (BP). An antibacterial agent that kills C. acnes bacteria through oxidation. Available in 2.5%, 5%, and 10% concentrations. The 2.5% works nearly as well as the 10% with less irritation. Bleaches fabric. Cannot build bacterial resistance, unlike antibiotics.

BHA (beta hydroxy acid). Salicylic acid is the main BHA used in skincare. BHAs are oil-soluble, meaning they can penetrate into pores to dissolve sebum and dead skin cells from the inside. Better for oily, acne-prone skin than AHAs.

Blind pimple. A colloquial term for a deep, painful bump under the skin that never comes to a head. Usually a nodule or cyst. Don't try to pop these. They're too deep for extraction and you'll just cause scarring.

Ceramides. Lipids (fats) naturally found in the skin barrier. They help retain moisture and protect against irritants. Many moisturizers include ceramides to repair the barrier, which is especially useful when acne treatments are drying out your skin.

Closed comedone. A whitehead. A pore that's clogged with sebum and dead skin cells but the opening is closed over, so the contents aren't exposed to air. Appears as a small, skin-colored bump. Not inflamed.

Comedone (plural: comedones). The technical term for a clogged pore. Can be open (blackhead) or closed (whitehead). Comedones are non-inflammatory acne lesions.

Comedogenic. Likely to clog pores. Certain ingredients (coconut oil, cocoa butter, some silicones) are rated on a comedogenicity scale from 0-5. A comedogenic rating of 3 or higher means the ingredient is likely to cause breakouts in acne-prone skin.

Comedolytic. Something that breaks up or prevents comedones. Retinoids and salicylic acid are comedolytic. If a product is described as comedolytic, it helps unclog pores.

Cortisol. A stress hormone produced by the adrenal glands. Elevated cortisol stimulates oil production and inflammation, which can worsen acne. This is the biological link between stress and breakouts.

Cutibacterium acnes (C. acnes). The bacteria primarily responsible for inflammatory acne. Formerly called Propionibacterium acnes (P. acnes), renamed in 2016. Lives in hair follicles and feeds on sebum. Everyone has it on their skin, but it causes problems when pores are clogged and conditions allow overgrowth.

Cystic acne. Deep, painful, pus-filled lesions that form beneath the skin surface. The most severe form of acne. Often requires prescription treatment (oral antibiotics, hormonal therapy, or isotretinoin). Cystic acne has a high risk of scarring.

D-G

Dermatologist. A medical doctor specializing in skin conditions. Board-certified dermatologists completed medical school plus a 4-year dermatology residency. They can prescribe medications and perform procedures that estheticians and general practitioners cannot.

DHT (dihydrotestosterone). A potent androgen hormone converted from testosterone by the enzyme 5-alpha reductase. DHT is the primary hormonal driver of excess sebum production in acne-prone skin. Medications like spironolactone reduce DHT activity.

Double cleansing. A two-step cleansing method: first an oil-based cleanser (or micellar water) to dissolve sunscreen, makeup, and excess oil, then a water-based cleanser to clean the skin itself. Useful for acne-prone skin that wears sunscreen or makeup daily.

Emollient. A moisturizing ingredient that softens and smooths the skin by filling gaps between skin cells. Emollients include ingredients like squalane, shea butter, and cetyl alcohol. Different from humectants (which draw water in) and occlusives (which seal moisture in).

Erythromycin. A topical antibiotic sometimes used for acne, usually combined with benzoyl peroxide (as Benzamycin). Resistance is a growing concern, which is why it's rarely prescribed alone anymore.

Excoriation. Skin damage caused by picking or scratching. "Acne excoriee" is a condition where someone compulsively picks at their acne, causing wounds, scarring, and worsening of the original lesions. If you can't stop picking, talk to a doctor. It can be related to anxiety or OCD.

Exfoliant. Something that removes dead skin cells from the surface (or from within pores). Physical exfoliants use scrubbing particles. Chemical exfoliants (AHAs, BHAs) use acids to dissolve cell bonds. For acne-prone skin, chemical exfoliants are generally preferred because physical scrubbing can irritate inflamed skin.

Folliculitis. Inflammation of hair follicles, which can look like acne but has different causes (bacterial, fungal, or irritation-based). Not all bumps on your skin are acne. If "acne" treatments aren't working, it might actually be folliculitis.

Fungal acne. Not technically acne. The proper name is Malassezia folliculitis (see below). It's caused by an overgrowth of yeast, not bacteria. Looks like small, uniform, itchy bumps, usually on the forehead, chest, or back. Doesn't respond to standard acne treatments and needs antifungal treatment.

Glycemic index (GI). A measure of how quickly a food raises blood sugar. High-GI foods (white bread, sugar, soda) cause insulin spikes that stimulate oil production and skin cell growth, potentially worsening acne. Low-GI diets have been shown in studies to improve acne.

H-K

Hormonal acne. Acne driven primarily by hormonal fluctuations, particularly androgens. Common along the jawline and chin. In women and girls, it often flares around menstruation. Treatment may include hormonal approaches (birth control pills, spironolactone) in addition to topical treatments.

Humectant. A moisturizing ingredient that draws water from the environment (or deeper skin layers) into the outer skin. Hyaluronic acid, glycerin, and aloe vera are humectants. They hydrate but don't seal moisture in, so they work best layered under an occlusive or emollient.

Hyaluronic acid (HA). A humectant that can hold up to 1000 times its weight in water. Naturally present in skin. Applied topically, it plumps and hydrates the skin surface. Does not treat acne, but helps counteract the drying effects of acne treatments. Despite the name, it's not an exfoliating acid.

Hyperpigmentation. Darkening of the skin in patches or spots. In acne, this usually refers to PIH (post-inflammatory hyperpigmentation), the dark marks left after a pimple heals. More common and more persistent in darker skin tones. Sun exposure makes it worse.

IGF-1 (insulin-like growth factor 1). A hormone that stimulates cell growth, including the growth of sebocytes (oil-producing cells) and keratinocytes (skin cells). IGF-1 is elevated by high-glycemic diets and dairy consumption, which is one proposed mechanism for the diet-acne connection.

Isotretinoin. The generic name for the drug commonly known by its former brand name Accutane. An oral retinoid prescribed for severe, treatment-resistant acne. It dramatically reduces sebum production, shrinks oil glands, and can produce long-term or permanent remission of acne. Has significant side effects and requires monitoring. Must not be taken during pregnancy due to severe birth defects.

Keratolytic. Something that softens and helps dissolve the protein keratin, which makes up the outer layer of skin and can clog pores. Salicylic acid and urea are keratolytic agents. They work by loosening dead skin cells that would otherwise plug follicles.

L-N

Lesion. A general medical term for any abnormal area of skin. In acne, "lesion" refers to any individual pimple, comedone, nodule, or cyst. Dermatologists often count lesions to assess acne severity.

Macrocomedone. A large closed comedone, usually bigger than 1mm. These stubborn bumps often don't respond well to topical treatment alone and may need extraction by a dermatologist.

Malassezia. A genus of yeast that naturally lives on human skin. When it overgrows in hair follicles, it causes Malassezia folliculitis (commonly called "fungal acne"). Malassezia feeds on certain oils, so avoiding those oils in skincare products can help.

Microcomedone. The earliest, invisible stage of a clogged pore. Before you can see a blackhead or whitehead, the pore is already partially blocked at the microscopic level. Retinoids work partly by preventing microcomedone formation.

Moisturizer. A product that hydrates the skin and supports the skin barrier. Even oily, acne-prone skin needs moisturizer, especially when using drying acne treatments. The right moisturizer won't cause breakouts. Look for non-comedogenic, fragrance-free formulas.

Niacinamide. Vitamin B3. An anti-inflammatory ingredient that also helps regulate oil production, improve skin barrier function, and reduce hyperpigmentation. Generally well-tolerated and pairs well with most acne treatments. Found in concentrations of 2-10% in serums and moisturizers.

Nodule. A large, hard, painful lump deep under the skin. Nodules are a severe form of inflammatory acne. Unlike pustules, they don't contain pus that can be extracted. They require professional treatment, often oral medication.

Non-comedogenic. A product labeled as unlikely to clog pores. There's no standardized testing requirement for this claim in the US, so it's not a guarantee, but it's still a useful filter when shopping. Prefer non-comedogenic products for acne-prone skin.

O-R

Occlusive. A moisturizing ingredient that forms a physical barrier on the skin to prevent water loss. Petrolatum (Vaseline), dimethicone, and lanolin are occlusives. They seal moisture in but don't add moisture themselves. Despite myths, properly formulated occlusives don't cause acne.

Open comedone. A blackhead. A pore clogged with sebum and dead skin cells where the opening remains open. The dark color comes from oxidation of the contents when exposed to air, not from dirt.

OTC (over the counter). Available without a prescription. Adapalene 0.1%, benzoyl peroxide, and salicylic acid are all OTC acne treatments. Some effective treatments require a prescription (tretinoin, antibiotics, isotretinoin, spironolactone).

Papule. A small, red, raised bump on the skin without visible pus. Papules are inflammatory acne lesions. They happen when the wall of a clogged pore breaks and the immune system responds. Don't try to pop papules. There's nothing to extract.

PIE (post-inflammatory erythema). Red or pink marks left after a pimple heals. More common in lighter skin tones. Caused by dilated blood vessels or damaged capillaries in the healing area. Fades with time, but can last months. Different from PIH (which is brown/dark). Time, azelaic acid, and vascular lasers can help.

PIH (post-inflammatory hyperpigmentation). Dark brown or purple marks left after a pimple heals. More common and more visible in darker skin tones. Caused by excess melanin production triggered by inflammation. Can last months to over a year without treatment. Sunscreen, azelaic acid, retinoids, and vitamin C can help it fade.

Pore. The tiny opening on the skin's surface where a hair follicle exits. Sebum (oil) reaches the skin surface through pores. Pore size is mostly genetic and doesn't change with products, despite what marketing says. Pores don't "open" and "close."

Purging. A temporary increase in breakouts that happens when starting retinoids or certain exfoliants. These treatments speed up cell turnover, pushing existing microcomedones to the surface faster. Purging typically lasts 4-8 weeks and happens in areas where you normally break out. If new breakouts appear in areas you don't normally get acne, it's not purging, it's a reaction.

Pustule. A pimple with visible white or yellow pus at the surface. Pustules are inflammatory lesions that form when the body's immune response to a clogged, infected pore produces pus. These are what most people picture when they think "pimple."

Retinoid. A class of compounds derived from vitamin A. Includes tretinoin (prescription), adapalene (OTC and prescription), tazarotene (prescription), and retinol (OTC, weaker). Retinoids are considered the gold standard topical treatment for acne because they normalize cell turnover, reduce comedone formation, and have anti-inflammatory properties.

Retinol. A weaker, OTC form of retinoid. Less effective than tretinoin or adapalene for acne, but also less irritating. Found in many anti-aging products. If you have active acne, adapalene is a better choice than retinol.

S-Z

Salicylic acid. A BHA that exfoliates inside pores by dissolving sebum and dead skin cells. Available OTC in 0.5-2% concentrations in cleansers, toners, and spot treatments. Good for blackheads and whiteheads. Less effective than retinoids for inflammatory acne.

Sebaceous filament. A thin, column-shaped structure in pores that channels sebum to the skin surface. Commonly mistaken for blackheads, especially on the nose. Sebaceous filaments are normal and everyone has them. You can temporarily reduce their appearance with salicylic acid, but they'll always refill.

Sebaceous gland. The gland attached to each hair follicle that produces sebum (oil). Overactive sebaceous glands, driven by hormones, are a primary factor in acne development.

Sebum. The oily substance produced by sebaceous glands. Sebum naturally lubricates and protects the skin. In acne, excess sebum production and changes in sebum composition contribute to clogged pores and bacterial growth.

Skin barrier. The outermost layer of the skin (stratum corneum) that protects against water loss, bacteria, and irritants. Harsh acne treatments, over-washing, and physical scrubbing can damage the barrier, leading to dryness, sensitivity, and paradoxically, more breakouts. Moisturizers with ceramides and gentle cleansing help maintain it.

Spironolactone. An anti-androgen medication prescribed off-label for hormonal acne in women. It blocks androgen receptors, reducing oil production driven by hormones like DHT. Not used in males due to feminizing side effects. Usually prescribed at 50-200mg daily. Takes 2-3 months to see results.

Spot treatment. A product applied directly to individual pimples rather than the whole face. Benzoyl peroxide, salicylic acid, and sulfur are common spot treatment ingredients. Hydrocolloid patches (pimple patches) are another form of spot treatment.

SPF (sun protection factor). A measure of how well a sunscreen protects against UVB radiation. SPF 30 blocks about 97% of UVB rays. SPF 50 blocks about 98%. The difference above 30 is minimal. For acne-prone skin, SPF 30+ broad-spectrum sunscreen is recommended daily, especially when using photosensitizing treatments.

Stratum corneum. The outermost layer of the epidermis, composed of dead skin cells (corneocytes) held together by lipids. When these cells don't shed properly, they accumulate in pores and form comedones. Exfoliants and retinoids help normalize this shedding process.

Subclinical acne. Very small comedones that you can feel (as skin roughness or tiny bumps) but can barely see. Often the precursor to visible breakouts. Retinoids are effective at treating subclinical acne before it becomes visible.

Sulfur. An ingredient with antibacterial and keratolytic properties. Used in spot treatments and masks (like the De La Cruz sulfur ointment). Works well for some people, smells terrible. Less irritating than benzoyl peroxide for sensitive skin.

Topical. Applied directly to the skin, as opposed to "oral" (taken by mouth) or "systemic" (affecting the whole body). Topical acne treatments include retinoids, benzoyl peroxide, antibiotics, and acids.

Tretinoin. A prescription retinoid (brand names include Retin-A). Stronger than adapalene for many patients, but also more irritating. Available in cream and gel formulations at concentrations from 0.025% to 0.1%. Considered the reference standard for topical retinoids.

Wheal. A raised, often itchy bump caused by an allergic reaction or hives. Not acne, but sometimes confused with it. If your "acne" appeared suddenly, is very itchy, and the bumps move or change shape within hours, you might be having an allergic reaction.

Zinc. A mineral with anti-inflammatory and mild antibacterial properties. Zinc oxide in sunscreens provides UV protection. Oral zinc supplements (particularly zinc gluconate) have shown modest benefit for acne in some studies. Zinc pyrithione is used in antifungal products for conditions like dandruff and Malassezia folliculitis.

Bottom line

Skincare terminology sounds intimidating until you know what the words actually mean. This glossary covers the terms you'll encounter most often when reading about acne, shopping for products, or talking to a dermatologist. Bookmark it and come back whenever something trips you up. Understanding what adapalene, comedogenic, PIH, and retinoid mean puts you in a much better position to make informed decisions about your skin, and to cut through the marketing nonsense on product labels.

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Sources

1. Zaenglein AL, et al. Guidelines of care for the management of acne vulgaris. Journal of the American Academy of Dermatology. 2016;74(5):945-973. PubMed

2. Leyden JJ. A review of the use of combination therapies for the treatment of acne vulgaris. Journal of the American Academy of Dermatology. 2003;49(3 Suppl):S200-S210. PubMed

3. Thiboutot DM, et al. Practical management of acne for clinicians: An international consensus from the Global Alliance to Improve Outcomes in Acne. Journal of the American Academy of Dermatology. 2018;78(2 Suppl 1):S1-S23. PubMed

4. American Academy of Dermatology. Acne: Overview. AAD

5. Kraft J, Freiman A. Management of acne. Canadian Medical Association Journal. 2011;183(7):E430-E435. PubMed