A nurse in a delivery room writes “M” or “F” on a chart. In most cases the choice is unambiguous. In a small but not negligible fraction of births, the choice is not unambiguous, and the response — by medicine, by family, by the legal system, and by the affected person across the subsequent decades — has been one of the more contested questions in late-twentieth-and-early-twenty-first-century medical ethics.

Intersex (English: intersex, DSD — disorders or differences of sex development, VSD — variations of sex development; Japanese: インターセックス, intā-sekkusu; 性分化疾患, seibunka-shikkan; older: 半陰陽, han-in-yō) names the broad category of biological variation in sex characteristics — chromosomes, gonads, hormones, internal reproductive structures, and external genitalia — that does not fit neatly into typical male-or-female classification at birth. The category covers a substantial range of distinct medical conditions with substantially different developmental backgrounds, presentations, and clinical considerations.

This entry covers the major intersex conditions, the terminology debate around disorders / differences / variations, the international human-rights framework around the ethics of infant surgical intervention, and the Japanese clinical-and-legal context.

Distinction in vocabulary

The English-language terminology for the category has shifted multiple times across the past 75 years, and the contemporary state of the vocabulary is contested.

The traditional medical-Latin term hermaphroditism operates from the nineteenth-century medical-literature onward and is widely regarded as outdated and stigmatising in contemporary use. The term survives in some historical contexts and in continued (but contested) use in some non-English-language traditions.

Intersex emerged in early-twentieth-century biology and consolidated as the community-self-identification term in the late-twentieth-century rights-advocacy organisation work of the Intersex Society of North America (ISNA, founded 1993) and successor organisations including InterACT. The term emphasises identity and bodily-variation rather than pathology.

Disorders of Sex Development (DSD) was proposed in the 2005-2006 Chicago Consensus Conference on intersex clinical management (Lee et al., 2006) as a clinical-replacement term for the older clinical vocabulary. The term has been widely adopted in clinical medical writing but has been criticised by intersex rights advocates for retaining the “disorder” framing that the advocacy organisations argue inappropriately medicalises the variation.

Differences of Sex Development and Variations of Sex Development (VSD) are advocacy-side replacement terms that retain the DSD acronym but replace “Disorders” with “Differences” or “Variations”. These variants are increasingly common in advocacy organisations’ publications and have entered some clinical writing.

The Japanese vocabulary similarly carries the debate: intā-sekkusu (インターセックス, identity-emphasising loanword) and seibunka-shikkan (性分化疾患, “sex-differentiation disorder”, clinical-Japanese standard) operate in parallel, with the older Japanese term han-in-yō (半陰陽, “half-yin-yang”) substantially declined in contemporary use.

Major conditions

Intersex is not a single condition but a category covering a range of distinct medical conditions with substantially different developmental backgrounds. The major recognised conditions:

Congenital adrenal hyperplasia (CAH)

CAH is an autosomal-recessive genetic condition affecting adrenal cortisol synthesis. Inadequate cortisol production triggers compensatory excess adrenal androgen production. In XX (genetically-female) foetuses, the excess androgen drives external-genital masculinisation: enlarged clitoris, partially-fused labia, urethral-and-vaginal-opening modification. Incidence is approximately 1 in 15,000 births, making CAH one of the more common intersex conditions. Severe forms can produce life-threatening salt-wasting crisis in the neonatal period and require lifelong glucocorticoid replacement.

Androgen insensitivity syndrome (AIS)

AIS is an X-linked genetic condition affecting androgen-receptor function. XY (genetically-male) foetuses produce normal testosterone but the tissues do not respond to it. The complete form (CAIS) produces apparently-female external genitalia at birth, with the internal anatomy including intra-abdominal testes; the typical clinical pathway is female sex-assignment-at-birth with the underlying condition often not diagnosed until adolescence (when expected menstruation does not occur). The partial form (PAIS) produces variable external-genital presentation across a spectrum.

Klinefelter syndrome (XXY)

Karyotype 47,XXY. Phenotypically male individuals with reduced testicular function, often-elevated stature, often-reduced fertility, and variable presence of gynaecomastia (breast tissue development). Whether Klinefelter syndrome is classed as intersex depends on the definition framework; the syndrome is included in some clinical-DSD classifications but not in all advocacy-side intersex classifications.

Turner syndrome (X0)

Karyotype 45,X. Phenotypically female individuals with ovarian dysgenesis, short stature, and various-degree fertility limitation. As with Klinefelter, the inclusion of Turner syndrome in the intersex category depends on the framework.

5α-reductase deficiency

XY foetuses with inadequate 5α-reductase enzyme function show normal testosterone but inadequate dihydrotestosterone (DHT) production. External genitalia develop in a female-typical or ambiguous form at birth; at puberty, the rising testosterone produces external-genital masculinisation. The condition has been characterised at high frequency in a Dominican Republic population study (the “güevedoces” — “twelve-year-old penis” — village population), with broader documentation of similar genetic clusters elsewhere.

Other conditions

Ovotesticular DSD (formerly “true hermaphroditism”): individuals with both ovarian and testicular tissue. Rare. Swyer syndrome (XY gonadal dysgenesis): XY individuals with non-functional gonadal streaks who develop female-typical external genitalia. MRKH syndrome: XX individuals with congenital absence of the uterus and upper vagina. The complete intersex-category catalog is more extensive than this brief sample suggests.

Prevalence

The estimated prevalence of intersex conditions varies enormously depending on the inclusion criteria. Broad definitions (Fausto-Sterling 2000; Blackless et al. 2000) that include any non-typical variation in chromosomes, hormones, or genital anatomy place the figure at approximately 1.7% of all births. Narrower definitions restricted to clinically-significant external-genital atypicality place the figure at 0.02-0.05% of births (approximately 1 in 2,000 to 1 in 5,000).

The wide spread in prevalence estimates reflects the inherent definitional question: where to draw the line between “typical sex characteristics” and “atypical sex characteristics” is itself contested. The narrower definitions concentrate on cases where the sex-assignment-at-birth process is medically difficult; the broader definitions include the much wider range of biological variation across the human population.

Surgical intervention and human rights

The central ethical question in contemporary intersex clinical-practice is the appropriateness of surgical intervention on intersex infants and young children to “normalise” their external-genital appearance to typical-male or typical-female form. The historical practice — common across Anglophone and European clinical contexts from the mid-twentieth century onward — involved early surgical intervention based on family-and-physician judgment, with the goal of producing socially-typical appearance and reducing future-distress.

Adult intersex individuals raised under this clinical paradigm have, from the 1990s onward, organised in advocacy networks (ISNA, InterACT, OII Europe, others) and have documented substantial negative outcomes from non-consensual infant surgical intervention: physical complications, loss of sexual sensation, mismatched gender-identity-and-assigned-sex outcomes, and substantial psychological distress at the discovery of the underlying condition and the non-consensual intervention.

The UN Human Rights Council (2013, 2019 reports) has characterised non-consensual infant surgical intervention on intersex children as a “harmful practice” and has recommended the postponement of non-emergency surgical intervention until the affected person has decision-making capacity. Germany legislated against unnecessary intersex-infant surgery in 2021; Malta, Iceland, Portugal, and Greece have parallel legislation. The Japanese clinical and legal context has not produced equivalent legislation; the contemporary Japanese clinical practice continues with substantial physician-and-family discretion in surgical-intervention decisions.

Intersex and ふたなり (futanari)

The Japanese vernacular vocabulary futanari (ふたなり) refers, in the contemporary adult-content vocabulary, to fictional characters typically depicted with female-coded appearance and the addition of a functional penis. The fictional adult-content category is conceptually distinct from real-world intersex conditions: the adult-content depiction follows exaggerated-and-stylised fantasy conventions rather than the diverse anatomical realities of actual intersex conditions. Intersex advocacy literature emphasises that the conflation of fictional futanari depiction with real-world intersex experience is inappropriate and contributes to misunderstanding of the actual intersex population.

This entry treats intersex as a real-world medical-and-rights category. The dedicated futanari entry covers the separate fictional-content category.

Japanese context

The Japanese clinical vocabulary for intersex traditionally used han-in-yō (半陰陽) in older medical-and-legal writing; the term has substantially declined in contemporary use and has been replaced by intā-sekkusu (intersex) in identity-emphasising contexts and seibunka-shikkan (DSD) in clinical writing.

Japanese clinical-practice tradition has historically given substantial discretion to physicians and families in surgical-intervention decisions for intersex infants, with the broader UN-and-EU regulatory framework not yet translated into Japanese legislation. The Japanese intersex-rights community has organised through online communities, patient-support groups, and increasingly visible media coverage from the 2010s onward, with continuing advocacy for Japanese legislative response to the international human-rights consensus on non-consensual intervention.

Related Terms

• Futanari — separate fictional-content category
• Sex hormones
• Vagina (chitsu)
• Penis (inkei)
• Bisexual
• Asexual
• Newhalf — adjacent but distinct gender-identity category