Intersex is a term for people born with reproductive or sexual anatomy that doesn’t fit neatly into male or female categories. This can involve differences in genitals, chromosomes, hormones, or internal reproductive organs. Being intersex can present in roughly 40 different ways, ranging from visible differences at birth to variations that don’t become apparent until puberty or even later in life.
What Makes Someone Intersex
Sex development is usually described as binary: XY chromosomes lead to male anatomy, XX chromosomes lead to female anatomy. In reality, this process involves a complex chain of genetic signals, hormone production, and tissue responses. When any link in that chain works differently, the result can be a body that doesn’t fit the typical male or female pattern.
Intersex traits can show up in three main areas. The first is chromosomes: instead of the typical XX or XY, a person might carry XXY or another combination. The second is gonads, meaning the ovaries or testes may develop in unexpected ways or contain both types of tissue. The third is genitals, which may not look clearly male or female, or may not match what’s happening internally. Some people have a combination of all three.
The underlying causes vary. Some intersex traits result from changes to a gene that controls how the body responds to hormones like testosterone. Others happen because of unusual hormone exposure during embryonic development, either from the body’s own glands or from external sources. In some cases, a key gene responsible for triggering male development is missing, misplaced, or duplicated onto the wrong chromosome.
How Common Intersex Traits Are
You may have seen the figure that 1.7% of people are born intersex, a number popularized by biologist Anne Fausto-Sterling. That estimate, however, includes chromosomal conditions like Klinefelter syndrome (47,XXY) and Turner syndrome (45,X) that many clinicians don’t classify as intersex because the people who have them typically develop clearly male or female anatomy. Using a stricter definition, where chromosomal sex is inconsistent with physical sex or the body can’t be classified as either male or female, the prevalence is closer to 0.018%. The true number depends heavily on which conditions you count, and that question remains genuinely debated.
Conditions That Fall Under the Intersex Umbrella
Androgen Insensitivity Syndrome
A person with complete androgen insensitivity has XY chromosomes and testes, but their cells cannot respond to testosterone at all. Because testosterone can’t do its usual work, the body develops female-typical external anatomy. Internally, though, there is no uterus. The testes remain inside the abdomen, menstruation never occurs, and the person is infertile. Many people with this condition grow up identifying as female and don’t learn about it until puberty, when periods never arrive. Partial forms exist too, producing anatomy that blends male and female characteristics to varying degrees.
Congenital Adrenal Hyperplasia
In this inherited condition, the adrenal glands produce unusually high levels of androgens. For someone with XX chromosomes, this can masculinize the genitals during fetal development, so the baby may be born with anatomy that looks ambiguous. The classical form causes noticeable genital differences at birth in roughly 5% of cases and is one of the more commonly diagnosed intersex conditions.
5-Alpha Reductase Deficiency
This condition produces some of the most dramatic changes at puberty. Children with XY chromosomes are born with genitals that appear female or ambiguous because their bodies can’t efficiently convert testosterone into a more potent form needed for typical male genital development in the womb. At puberty, rising testosterone levels partially compensate: the voice deepens, muscle mass increases, the phallus grows, and testes may descend. In some communities where this condition clusters, these children are raised as girls and then transition socially during adolescence.
Ovotesticular Differences
The rarest form involves a person who has both ovarian and testicular tissue in the same body. About two-thirds of affected individuals have a combined gonad called an ovotestis. The most common chromosomal pattern is 46,XX, and in about 10% of those cases, a gene that normally triggers male development has been relocated onto the X chromosome. Babies with this condition are typically born with ambiguous genitalia.
When Intersex Traits Are Discovered
Some intersex traits are obvious at birth because the baby’s genitals look different from what’s expected. Others are invisible until puberty, when expected changes either don’t happen or unexpected ones do. A teenager with complete androgen insensitivity might see a doctor because menstruation never starts. Someone with 5-alpha reductase deficiency might experience sudden masculinization during adolescence. And some intersex traits, particularly chromosomal variations, are only discovered incidentally during fertility testing or genetic screening in adulthood.
Terminology: Intersex vs. DSD
In clinical settings, the term “differences of sex development” (abbreviated DSD) has largely replaced “intersex.” Medical sources like MedlinePlus now describe intersex as an older term for DSD. The shift happened in 2006 when a medical consensus group proposed the new language, partly to standardize diagnosis and partly because some families found the word “intersex” confusing or stigmatizing.
The change hasn’t been universally welcomed. Many intersex adults and advocacy organizations prefer “intersex” because it’s straightforward, avoids framing their bodies as disordered, and has become a recognized identity term. Some medical institutions now use the phrasing “differences” rather than “disorders” of sex development as a compromise. Which term you encounter depends largely on whether the context is clinical or community-based.
The Surgery Debate
One of the most contentious issues in intersex healthcare is whether to perform surgery on infants born with ambiguous genitals. For decades, the standard practice was to surgically assign a sex early in life, often before the child could participate in the decision. The rationale was that a clearly male or female appearance would make social development easier.
Intersex advocacy groups have pushed back strongly, arguing that irreversible cosmetic surgery on infants causes lasting physical and psychological harm and violates bodily autonomy. Several countries and jurisdictions have introduced restrictions on non-medically-necessary genital surgeries for intersex children. Professional urology societies have generally stopped short of endorsing a complete surgical moratorium, instead recommending that decisions be made by multidisciplinary teams and, whenever possible, delayed until the individual can participate in the choice. The tension between early intervention and informed consent remains one of the defining ethical questions in this area of medicine.