How to Choose a Serum

First: a serum is a format, not a promise

There is no regulatory definition of a serum and no required ingredient. In practice it means a thin, fast-absorbing, water- or silicone-based vehicle carrying a higher concentration of one or two actives and not much else — which is precisely why “serum” printed on a box is not information. A hyaluronic acid serum, a retinol serum and a salicylic acid serum have almost nothing in common except viscosity.

That has a useful consequence: you never shop for “a serum.” You shop for an active, and the serum is just the shape it arrives in. Once you accept that, the aisle stops being overwhelming, because most of what is written on the front of the bottle becomes irrelevant and the only part that matters is the ingredient list.

Step 1: name one goal, in one word

Not “better skin.” One of these: dehydration, oil, redness, breakouts, dullness, dark spots, fine lines, texture. The reason to insist on one is practical — a serum’s whole advantage is that it concentrates on a single problem, and a routine built around three goals at once is how people end up with an irritated barrier and no idea which product did it.

If the honest answer is “my skin is tight, flaky and sensitive,” your goal is not a serum at all — it is a gentler cleanser and a better moisturizer. Barrier problems are solved at the cleanse and moisturize steps, and adding a concentrated active to compromised skin reliably makes it worse. See how to repair your skin barrier first; the serum can wait a month.

Step 2: match the goal to the active

This is the entire decision, and it is a table rather than a philosophy. Each active below has a published evidence base for the goal next to it — the sources at the foot of this page are the reviews behind those claims.

One warning about that last row. Peptides have a real evidence base — a 2024 systematic review covers signal, carrier and neurotransmitter-affecting topical peptides — but it is a more modest one than retinol’s, and peptide marketing is the most oversold corner of the serum aisle. Treat them as a pleasant supporting act, not a retinoid substitute.

Step 3: check whether the strength is printed on the bottle

This is the filter that eliminates most of the shelf, and it is the one this site cares about most. Some brands state exact concentrations — The Ordinary, Paula’s Choice, Naturium, Good Molecules. Most do not, including nearly every drugstore retinol and almost all peptide serums. A missing number is not automatically disqualifying: a formulator has legitimate reasons not to publish, and plenty of unquantified serums are good. But it does mean you are buying on trust rather than on evidence, and you should know which one you are doing.

Where a number exists, more is not better. Niacinamide is the clearest example: most of the published benefit for redness and barrier function appears around 4–5%, yet the popular serums state 10% and 12%. Higher means more irritation risk rather than more benefit. The same logic applies to retinol — a 0.1% used three nights a week for a year does more than a 1% abandoned in week three — and to acids, where pH matters as much as percentage and almost nobody publishes it. Our niacinamide percentages and retinol strengths guides go through the numbers.

Step 4: read the three things that are not the active

Fragrance. A serum sits on your face for hours and carries a concentrated active. It is the worst possible place to add an ingredient that does nothing for your skin and is a leading cause of cosmetic contact allergy. Fragrance-free is the default, and the category offers plenty of it.

Packaging, for the unstable actives.This matters for exactly one family: L-ascorbic acid in water oxidizes on exposure to air and light, which is why an opaque bottle with a pump or a dropper beats a clear jar, and why some brands use anhydrous or derivative forms instead. It is not a general rule — niacinamide and peptides do not care. See why vitamin C serums turn brown for what oxidation looks like in the bottle.

Texture, honestly assessed.The best serum is the one you will still be using in three months, and texture is the main reason people stop. A tacky hyaluronic acid serum that pills under sunscreen, a gritty vitamin C suspension, an oil serum that will not sit under makeup — those are real reasons to choose differently, not vanity. If you have had products ball up on you, see why skincare pills.

Where the serum goes in your routine

Thinnest to thickest, which for most routines means: cleanse, serum on damp skin, moisturizer, then sunscreen in the morning. The AAD’s ordering guidance follows the same thin-to-thick logic, and the reason it works is mechanical rather than mystical — a water-light serum cannot get through an occlusive cream, and a cream has no trouble going on over a serum.

Two exceptions worth knowing. A hyaluronic acid serum wants damp skin and a moisturizer directly on top, or in very dry air it can pull water out of your skin rather than into it. And a retinoid on dry skin often does better sandwiched: thin moisturizer, retinoid, moisturizer again. Full detail in skincare routine order and how to layer skincare; for what can share a night, see the ingredient conflict chart.

The five ways people choose a serum badly

Buying three at once. You learn nothing and risk everything. One new active, four weeks, then decide.

Buying for a goal the format cannot serve. No serum firms sagging skin, closes a pore permanently, or substitutes for sunscreen.

Buying the highest percentage available. More active means more irritation, and irritated skin looks worse than untreated skin.

Buying a serum instead of a moisturizer. A serum under-moisturizes by design. Oily skin needs a light moisturizer, not none.

Buying on the front of the box.“Brightening,” “firming” and “glow” are outcomes, not ingredients. Turn the bottle around; the ingredient list is where the information is.

If you want the short version: pick your one goal, find its active in the table above, buy the cheapest version that states its concentration and leaves out the fragrance, and use it for three months before you buy anything else. That approach costs less than one prestige serum and will teach you more about your own skin than a cabinet full of them. Browse the whole shelf by active in serums & actives.