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noun Uncommon

serum

SEER-um
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Serum (noun) means a thin, lightweight skincare product, usually applied after cleansing and before a heavier cream, formulated to carry a high proportion of active ingredients in a small amount of liquid. Example: “She kept the serum on the shelf above the sink and used it before her moisturiser.”

noun
1
A thin, lightweight skincare product, usually applied after cleansing and before a heavier cream, formulated to carry a high proportion of active ingredients in a small amount of liquid.
"She kept the serum on the shelf above the sink and used it before her moisturiser."
"Two drops of serum were enough for his whole face."
"Pat the serum gently into your skin before putting on moisturiser."
2
technical In medicine, the clear pale fluid that separates from blood when it clots, containing no cells and no clotting proteins. It is the part of a blood sample many laboratory tests are run on.
"The lab measured cholesterol in the patient's serum."
"Serum was separated from the sample before testing."
"The technician spun the blood sample to collect the serum for testing."
3
technical A preparation made from the blood of a person or animal that carries antibodies, given to provide immediate protection against a poison or infection.
"Antivenom serum was flown to the hospital overnight."
"The doctor gave the patient serum to fight the infection quickly."
"Years ago, serum from immunised horses was used to treat snake bites."

How to use serum

Learner’s notes

In plain EnglishEither a thin, strong-smelling skin liquid you put on before cream, or the clear part of blood left after it clots.

When to use it

The skincare sense is everyday; the blood senses are technical and belong to medicine and laboratory science. The plural is serums or, in scientific writing, sera.

Memory tip

Context decides the meaning entirely: on a bathroom shelf it is a cosmetic, in a hospital report it is a blood fraction.

Trace the full origin ↓
Easily confused with
plasma → essence → toner → emulsion →
Common pairings
face serum vitamin C serum serum sample serum levels hair serum
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She kept the _____ on the shelf above the sink and used it before her moisturiser.

Etymology

From Latin serum, meaning whey or watery fluid.

Origin: Latin

Synonyms

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treatment essence concentrate booster blood serum antiserum

Related words

heart center effect centre treatment focus contract spirit

Frequently asked questions

What is the difference between a serum and a moisturiser?
A serum is thin and is built to deliver a concentrated dose of specific ingredients; a moisturiser is generally richer and is built to soften the skin and slow water loss from its surface. They sit at different points in a routine, with the lighter serum going on first.
Is serum the same as plasma?
No. Plasma is the liquid part of blood including the clotting proteins; serum is what remains after blood has clotted, so the clotting proteins are gone. Laboratories treat the two as different sample types.
Why are serums sold in such small bottles?
Because they are concentrated and are applied in very small amounts, often a few drops. Bottle size reflects how the product is dosed rather than how long it lasts.
What is the meaning of serum?
"serum" (noun) means a thin, lightweight skincare product, usually applied after cleansing and before a heavier cream, formulated to carry a high proportion of active ingredients in a small amount of liquid.

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