Sex vs Gender: What's the Difference?

Sex refers to a set of biological attributes: chromosomes, hormones, gonads and anatomy. Gender refers to the socially constructed roles and expectations attached to those categories, and to a person's own internal sense of who they are. The two usually line up. When they do not, you need both words to describe what is happening.

What is the difference between sex and gender?

The World Health Organization draws the line this way. Sex is "a set of biological attributes in humans and animals", including "chromosomes, gene expression, hormone level and function, and reproductive and sexual anatomy". Gender refers to "socially constructed characteristics of women and men, such as norms, roles and relations", and the WHO adds that these "vary from society to society and evolve over time".

Gender identity is a third thing again, and the WHO defines it separately: "a person's innate, deeply felt internal and individual experience of gender, which may or may not correspond to the person's physiology or designated sex at birth".

The practical consequence is that "male" and "female" are answers to a question about bodies, while "man" and "woman" are answers to a question about people. Most of the time nobody notices the difference, because the answers match. The distinction becomes load-bearing when they do not.

Sex vs gender: side by side

	Sex	Gender
What it refers to	Biological attributes: chromosomes, hormones, gonads, anatomy	Social roles, norms and expectations, plus a person's internal sense of self
Typical terms	Male, female, intersex	Man, woman, non-binary, and many culturally specific categories
Who determines it	Assigned at birth, usually from external anatomy	Known by the person; expressed and read socially
Does it vary between cultures?	The biology does not; how it is categorised and recorded does	Yes, substantially. Categories, roles and the number of recognised genders differ across societies
Can it change?	Some attributes can be medically altered; chromosomes cannot	A person's gender identity is generally stable, though some people are fluid; the social expectations attached to gender change constantly
Relevant abbreviation	AFAB, AMAB, AISAB (assigned female / male / intersex at birth)	Cis, trans, non-binary
Says anything about attraction?	No	No. Sexual orientation is a third axis again.

Is sex a binary?

Not cleanly, and the reason is intersex people: people born with variations in sex characteristics that do not fit standard definitions of male or female. See our intersex entry.

How many people that is depends entirely on what you count, and this is where a lot of internet argument comes from. Two published figures get quoted:

About 1.7%, from Blackless and colleagues (2000) in the American Journal of Human Biology. This uses a broad definition, counting any deviation from an idealised male or female, including late-onset congenital adrenal hyperplasia and sex chromosome variations that do not involve ambiguous genitalia at birth.
About 0.018%, from Sax (2002) in The Journal of Sex Research, responding directly to that paper. Sax uses a narrower clinical definition, counting only conditions "in which chromosomal sex is inconsistent with phenotypic sex, or in which the phenotype is not classifiable as either male or female", and excludes the categories above.

Both numbers are real. They answer different questions, and neither one is the number. What matters for this page is the thing both authors agree on: people are born whose bodies do not sort neatly into two boxes, and no definitional argument makes them disappear. Intersex organisations, including OII Europe, generally argue that the more urgent issue is not the count but the continued practice of non-consensual surgery on intersex infants.

Why does the distinction matter in practice?

Mostly because forms, laws and clinics conflate the two, and people fall through the gap.

Healthcare. A trans man may need cervical screening. A trans woman may need prostate checks. Systems that record only one field get this wrong.
Documents. Belgium has allowed a gender marker change without medical requirements since the 2017 transgender law, and the Constitutional Court ruled in 2019 that the absence of an option beyond M and F was discriminatory. That gap has still not been closed by legislation.
Research. Studies that record "sex" and mean "gender", or the reverse, produce data nobody can interpret.
Everyday language. Most people say "sex" when they mean "gender" and nothing bad happens. The distinction is a tool for when precision is needed, not a rule for casual conversation.

Which word should I use?

Use whichever one matches what you actually mean. If you are talking about bodies, biology, medicine or anatomy, sex is the right word. If you are talking about who someone is, how they live, or how they are addressed, gender is the right word. If you are unsure, gender is more often correct in everyday conversation, because most of the time you are talking about people rather than gonads.

When it is about a specific person, the reliable move is to use their own words for themselves. Nobody is offended by being described the way they describe themselves.

Questions people ask

Is gender just a social construct?

The social roles attached to gender are constructed, and they clearly vary between societies and change over time. Gender identity, meaning a person's internal sense of their own gender, is not something they chose or that a society handed them, and the WHO describes it as innate. Both statements can be true at once.

Is sex assigned or observed?

Both words are defensible. "Observed" describes what the clinician does. "Assigned" describes what the record does, and it is the standard term because the observation is turned into a legal category with lifelong consequences. The abbreviations AFAB and AMAB come from that usage.

Does this mean biology is not real?

No. Chromosomes, hormones and anatomy are real and they matter, particularly in medicine. The claim on this page is narrower: that biological sex and social gender are two different things that usually correlate, and that treating them as one word produces errors.

What about gender expression?

That is a fourth thing: how someone presents, through clothing, voice, hair and mannerism. It is not a reliable guide to gender identity, and it is not a guide to sexual orientation at all. See key distinctions.