The Ingredient Glossary: 25 Ingredients, One Line Each
Twenty-five ingredients, grouped by what they actually do, one line each. This isn't a list to memorize. It's a page to search when a label has a word on it you don't recognize, and it's the routing table for the rest of this library: almost every entry links to the Foundation or File that covers it properly.
A scary name is not a red flag and a familiar one is not automatically safe. Position on the label and the actual job an ingredient does matter more than how the word sounds, which is the whole argument of how to read a label.
Four groups: the ingredients worth knowing on sight, the actives that actually treat something, the ingredients that support the skin barrier, and the small handful worth watching for on a list. Every entry is roughly one line. Nothing here needs memorizing before it's useful.
Worth knowing
These are the ingredients that show up constantly, get discussed the most, and are worth recognizing on sight even before deciding whether a specific product is worth buying. None of them are dangerous. A few are genuinely useful before 18, and a few are mostly sold for a job that doesn't exist yet at this age.
Niacinamide. A form of vitamin B3, and the one active that reliably earns its place before 18: it supports oil balance and the look of pores without the irritation profile of stronger actives. It's the working ingredient in pore magic.
Vitamin C (ascorbic acid). An antioxidant that can help with the look of dullness and uneven tone over time. Genuinely useful, notoriously unstable in a bottle, and a "nice to have" rather than a routine essential at this age.
Peptides. Short chains of amino acids marketed heavily for firmness and fine lines, neither of which is a teenage skin concern. Not harmful, just usually sold for a job that doesn't exist yet at this age.
Centella (Centella asiatica). A calming plant extract with a real reputation for soothing irritated skin. A reasonable ingredient to see on a label for reactive or recovering skin, not a cure for anything on its own.
Zinc oxide. A mineral sunscreen active that physically blocks UV rather than absorbing it. Our standard, and the only kind worth buying: non-nano, fragrance-free, checked on the inactive list too. See our Sun & SPF collection.
Titanium dioxide. The other mineral sunscreen active, usually paired with zinc oxide. Same standard applies: non-nano, and the whole label matters, not just the active ingredient line. More on the mechanism in how sunscreen actually works.
The actives
An active does a specific, named job rather than just supporting the skin generally, which also means it's the category most likely to irritate if it's overused or stacked with two or three others at once. The four-step acne mechanism is the map worth keeping in mind here: most of these work on one specific step, and none of them work on all four at once, whatever the label implies.
Salicylic acid. A beta hydroxy acid that gets inside the pore to clear it, which is a genuinely useful job against blackheads and blocked pores. The working ingredient in smooth sali, and appropriate once breakouts actually start.
Benzoyl peroxide. Acts on the bacteria step of a breakout, and it's one of the better-studied over-the-counter acne ingredients there is. Real, effective, and worth pairing with a fragrance-free moisturizer since it can be drying.
Adapalene. A retinoid that treats acne specifically, available over the counter at 0.1% since 2016. A legitimate option for real, diagnosed breakouts, and a completely different conversation from cosmetic anti-aging retinol.
Retinol. A vitamin A derivative that speeds up cell turnover, which is genuinely useful on skin where turnover has slowed. Adolescent skin hasn't slowed yet. The full case for waiting is its own File.
AHA (alpha hydroxy acid). Surface exfoliants like glycolic and lactic acid that work on the skin's top layer. Useful in small, occasional doses; easy to overdo, and overdoing it is a common source of irritation in stacked routines.
BHA (beta hydroxy acid). The category salicylic acid belongs to. Oil-soluble, which is why it can get inside a pore rather than just working on the surface the way an AHA does.
Azelaic acid. A gentler acid that helps with both breakouts and the look of post-acne marks, with a lower irritation profile than most alternatives. A reasonable option for sensitive, acne-prone skin at any age past the basics.
Sulfur. An old-school acne ingredient that dries out blemishes directly. Effective for spot treatment, has a distinct smell most formulas now mask, and isn't something to layer over the whole face daily.
Tea tree oil. A plant-derived antimicrobial with some real evidence against acne-causing bacteria, though generally weaker and slower than benzoyl peroxide. Worth patch testing, since it's also a common cause of contact irritation.
The barrier ingredients
Nothing in this group treats acne or does anything dramatic on its own, which is exactly why it's the most consistently underrated category on any label. The Moisturizer File covers why these ingredients matter for every skin type, oily included, in more depth than a one-line entry can.
Hyaluronic acid / sodium hyaluronate. A humectant that pulls water into skin. Sodium hyaluronate is the salt form and absorbs slightly better. Neither treats a breakout; both support the hydration a barrier needs to function.
Ceramides. Lipids that are literally part of what holds the skin barrier together. One of the most evidence-backed barrier ingredients there is, and a genuinely good sign on a moisturizer label at any age.
Glycerin. A humectant, cheap, unglamorous, and one of the most reliably effective hydrating ingredients in skincare. Its ordinariness is not a mark against it.
Squalane. A lightweight emollient that mimics skin's own natural oils without feeling heavy. A common, sensible choice in a fragrance-free moisturizer for any skin type, oily included.
Panthenol. Provitamin B5, used for its soothing and moisture-binding properties. A common, low-risk addition to a barrier-focused product, not an active in its own right.
Allantoin. A soothing, skin-conditioning ingredient often paired with panthenol. Gentle, low risk, and mostly there to calm a formula rather than treat anything specific.
Urea. A humectant that, at higher concentrations, also has a mild exfoliating effect on very dry or rough skin. At the low concentrations used in most facial moisturizers, it's simply a hydrator.
Dimethicone. A silicone that smooths texture and helps lock in moisture underneath it. Not the villain some clean-beauty content makes it out to be; it's inert on skin and a common, functional barrier ingredient.
The ones to watch
Only two entries make this list, on purpose. Most of what circulates as a scary ingredient turns out to be either harmless at the concentration used or already covered above as an active doing a real job. These two are the exceptions worth actually checking a label for.
Alcohol denat. (or SD alcohol). The drying kind of alcohol. High on an ingredient list, on young or already-irritated skin, it's worth a second look. Not the same ingredient as the fatty alcohols below, despite the shared word.
Fragrance / parfum. One word standing in for a formula's worth of undisclosed ingredients, and the single highest-yield thing to check for on any label. Our entire line skips it. The full case for why is here.
What this page doesn't do
A one-line entry tells you what an ingredient is and whether it generally makes sense at this age. It doesn't tell you the concentration in a specific product, where that ingredient sits on the label relative to the 1% line, or whether the rest of the formula around it is any good. Those are label-reading questions, not glossary questions, and that skill has its own Foundation.
It also doesn't replace an ingredient list you're actually holding in your hand. A product can combine three or four of the entries above in ways that interact, an exfoliating acid layered under a retinol, for instance, and this page describes each ingredient in isolation rather than how a specific formula behaves as a whole. When in doubt about a specific product, the ingredients here are a starting vocabulary, not a final verdict on what's in your hand.
This list will also grow. Twenty-five is a starting set, chosen because they're the ingredients that show up most often across the Foundations and Files already published, not because the category stops there. New entries get added as new Files need them.
Go deeper
For the mechanism these ingredients are acting on, read what actually causes acne. For the full case on any single ingredient flagged above, its own File or Foundation covers it in depth.
Dana
