Intersex is a term for people born with biological sex characteristics that don’t fit neatly into typical male or female categories. These variations can involve chromosomes, hormones, reproductive organs, or external anatomy. Intersex is not a gender identity but rather a set of natural biological differences that are present from birth. Estimates of how common it is vary widely, from about 0.018% of the population using a narrow clinical definition to as high as 1.7% when broader criteria are applied.
What Makes Someone Intersex
During fetal development, sex characteristics develop in stages: chromosomes direct the formation of gonads (ovaries or testes), which then produce hormones that shape internal and external anatomy. Intersex variations happen when there’s a difference at any point in this chain. A person might have one chromosomal pattern but develop physical features associated with a different sex, or their hormone levels might push development in an unexpected direction.
These variations take many forms. Some are visible at birth, like genitalia that don’t look typically male or female. Others are completely internal and invisible, only discovered later when puberty doesn’t progress as expected or when someone has difficulty conceiving. A few common examples help illustrate the range.
Common Intersex Variations
Androgen Insensitivity Syndrome
A person with complete androgen insensitivity syndrome (CAIS) has XY chromosomes and internal testes, but their body’s cells can’t respond to testosterone. The result is that they develop a typical female appearance, including breast development at puberty, but have no uterus and a shorter vaginal canal. They’re often raised as girls and may not discover the condition until they don’t get a period or have difficulty with fertility testing. Partial forms of this condition produce a wider spectrum of physical features, from mostly female to mostly male anatomy.
Congenital Adrenal Hyperplasia
Congenital adrenal hyperplasia (CAH) is one of the most common intersex-related conditions. It occurs when a missing enzyme causes the adrenal glands to underproduce cortisol and overproduce androgens (hormones that drive male-typical development). In girls born with CAH, the excess androgens during fetal development can enlarge the clitoris, partially fuse the labia, or merge the urinary and vaginal openings. Boys with CAH may show signs of very early puberty. Both sexes can experience rapid childhood growth followed by shorter-than-average adult height, and some face fertility challenges later in life.
Chromosomal Variations
Some intersex traits are rooted in having an atypical number of sex chromosomes. People with Turner syndrome have a single X chromosome instead of the usual two sex chromosomes, and typically develop as female but may not go through puberty without hormone support. Those with Klinefelter syndrome have XXY chromosomes, develop as male, and often aren’t diagnosed until adulthood when they experience low testosterone or infertility. Neither condition necessarily causes ambiguous anatomy, which is why they sometimes go undetected for years.
When Intersex Traits Are Discovered
Some intersex variations are apparent immediately at birth, when a baby’s genitalia don’t look clearly male or female. In these cases, medical teams typically run chromosomal and hormonal tests before a sex is recorded on the birth certificate. Prenatal genetic testing can also reveal a mismatch between chromosomal sex and the anatomy seen on ultrasound.
Many intersex people, though, don’t learn about their variation until much later. Puberty is a common point of discovery: a teenager might not menstruate, might develop breasts unexpectedly, or might not go through the changes their peers are experiencing. Some people don’t find out until adulthood, often during fertility evaluations. This means a significant number of intersex individuals grow up without knowing they have an intersex trait.
Intersex Is Not the Same as Gender Identity
This is where confusion often arises. Intersex describes the body you’re born with. Gender identity is your internal sense of being male, female, both, or neither. The two are separate things. Most intersex people identify as either male or female, consistent with how they were raised. Some identify as nonbinary or with a different gender than what was assigned to them, but that’s also true of people who aren’t intersex.
Intersex is also distinct from being transgender. A transgender person experiences a disconnect between their gender identity and the sex they were assigned at birth, but their biological sex characteristics are typically consistent with each other. An intersex person has biological features that are mixed or atypical, regardless of how they identify. Someone can be both intersex and transgender, but the two categories describe different things.
The Debate Over Early Surgery
For decades, the standard medical approach was to surgically alter intersex infants’ genitalia to look more typically male or female, often in the first months of life. Parents were sometimes advised to raise the child firmly in one sex and never discuss the surgery. This practice has come under intense scrutiny.
Current ethical guidelines from medical ethicists and intersex advocacy groups are clear: surgery on intersex infants should only happen when it’s medically necessary, such as when a condition blocks urinary function. Cosmetic genital surgeries, those done purely to make anatomy look more typical, should be delayed until the person is old enough to participate in the decision. The reasoning is straightforward. These procedures are irreversible, they can reduce sensation and sexual function, and the child may grow up to identify with a different sex than the one surgeons chose. The burden of proof, ethicists argue, should fall on anyone proposing surgery to demonstrate it truly serves the child’s wellbeing rather than adult discomfort with ambiguity.
In practice, this shift is uneven. Some medical centers have adopted more conservative, wait-and-see approaches. Others continue to perform early surgeries. Many intersex adults who underwent childhood procedures report negative outcomes, including loss of sensation, emotional distress, and a sense that the choice should have been theirs.
Legal Recognition
A growing number of countries have begun accommodating intersex people in legal documents. Australia introduced an “X” option on passports in 2011 for people who don’t identify as male or female. Germany changed its law in 2013 to allow the sex field on birth certificates to be left blank. Several other countries and some U.S. states have since adopted similar measures, though the specifics vary widely. These changes reflect a broader recognition that binary sex categories don’t account for everyone’s biology.
How Prevalence Is Counted
You’ll see very different numbers depending on the source, and it’s worth understanding why. The often-cited figure of 1.7% comes from biologist Anne Fausto-Sterling, who counted all conditions where sex development deviates from the typical path, including chromosomal variations like Klinefelter syndrome that may never cause noticeable symptoms. A narrower analysis by physician Leonard Sax, which counted only conditions involving genuinely ambiguous genitalia or a clear mismatch between chromosomes and anatomy, put the figure at about 0.018%, roughly 1 in 5,500 births. The real answer depends on where you draw the line, and there’s no universal agreement on that boundary. What’s not in dispute is that intersex variations are a naturally occurring part of human biology, not a disorder that needs to be “fixed.”