Serum

Delivers a high dose of actives in a thin fluid that goes on before anything heavier.

Measurement

Open-jar symbol often reads 3M to 12M

Serum

At a glance
Part of	Formulation
Measures	Open-jar symbol often reads 3M to 12M
Applies to	Skincare, Hair Care

The basics

What to know about serum

Serum is a marketing word rather than a regulated one. In practice it names a thin fluid carrying a higher share of active ingredients and fewer thickeners than a moisturizer. Concentration is the whole point, and it is why the percentage on the label matters more here than anywhere else in a routine. Vitamin C as L-ascorbic acid usually works between 10 and 20 percent, niacinamide between 4 and 10 percent, retinol between 0.1 and 1 percent.

Order of application follows viscosity: thinnest first. A serum on clean, slightly damp skin absorbs in under a minute, then a moisturizer over the top slows the water leaving and keeps the active in contact. Reverse that order and the cream blocks most of it at the surface. Give each layer about 30 seconds to settle rather than stacking them wet.

Strength cuts both ways. Retinoids and acids speed cell turnover and leave skin more sensitive to sun, so daily broad spectrum sunscreen is not optional alongside them. Starting two or three nights a week beats nightly until skin adjusts. Introduce one new active at a time and wait two weeks before adding another, or you will not know which one caused the flaking. Vitamin C oxidizes as well: once a clear serum turns deep yellow or brown it has lost potency and belongs in the bin. Anything painful, spreading or still unsettled after a few weeks is a question for a dermatologist rather than a new bottle.

In photos

Serum on real products

See this option on different products. Open a photo for a larger view, or select the name to read its guide.

01
Hair Care

Best for

When it works well

Targeting one specific concern suits serums, because you can dose a single active without changing the rest of the routine.
Layering under moisturizer works by design, as the thin fluid absorbs first and the cream seals it in.
Oily skin often prefers a serum to a cream, since hydration and actives arrive with almost no oil attached.
Anyone building a routine slowly gains here, because one serum can be added or dropped without disturbing anything else.

Used with

Products that use serum

Compare

Serum compared with every option

What physical form does the product take? Every option in formulation, drawn to the same scale. You are reading serum.

01
LiquidOpen-jar symbol often reads 6M to 12M
Pours thin and blends before it sets, which is why most foundations and tints take this form.
02
CreamOpen-jar symbol often reads 6M to 12M
Cushions dry skin with a thick oil and water blend that absorbs slowly.
03
GelOpen-jar symbol often reads 6M to 12M
Absorbs in seconds and layers without weight because water carries most of the formula.
04
PowderOpen-jar symbol often reads 12M to 24M
Lays down color dry and soaks up oil, so it finishes a base rather than starting one.
05
StickOpen-jar symbol often reads 12M to 24M
Twists up solid and goes on straight from the bullet, with no brush and no spill.
This entry
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SerumOpen-jar symbol often reads 3M to 12M
Delivers a high dose of actives in a thin fluid that goes on before anything heavier.