Intersex is an umbrella term for natural biological variations where a person’s chromosomes, hormones, gonads, or genitals don’t fit neatly into typical male or female categories. These variations are more common than most people realize. The United Nations estimates that roughly 1.7 percent of babies are born with some form of intersex trait, making it about as common as red hair.
How Sex Development Works
To understand intersex conditions, it helps to know that biological sex isn’t a single switch. It’s a series of steps during fetal development, each influenced by chromosomes, hormones, and how the body responds to those hormones. Typically, a fetus with XY chromosomes develops testes, which produce testosterone, which shapes male-typical anatomy. A fetus with XX chromosomes develops ovaries and female-typical anatomy.
But these steps can diverge in many ways. A person might have XY chromosomes yet develop female external anatomy because their body can’t respond to testosterone. Another person might have XX chromosomes but be exposed to unusually high levels of androgens (hormones that drive male-typical development), resulting in genitals that don’t look clearly male or female at birth. Some people have a mix of cells with different chromosome patterns, a phenomenon called mosaicism. Others carry an extra sex chromosome (XXY) or have only one (X alone). Each variation leads to a different set of physical characteristics.
Common Intersex Conditions
Congenital Adrenal Hyperplasia (CAH)
CAH is one of the most frequently diagnosed intersex conditions. It stems from a genetic change that leaves the adrenal glands unable to produce enough of an enzyme called 21-hydroxylase. Without it, the body can’t make adequate cortisol (a stress hormone), so it compensates by overdriving the adrenal glands. The side effect: a surge in androgens.
For girls born with classic CAH, this androgen excess during fetal development can cause an enlarged clitoris or external genitals that appear atypical. Boys with CAH are usually born without visible genital differences. Later in childhood, both boys and girls may develop early pubic hair, acne, and rapid growth spurts that paradoxically lead to shorter adult height because their growth plates close too soon. Teenage and adult women with CAH may experience irregular or absent periods, excess facial and body hair, and a deeper voice.
Androgen Insensitivity Syndrome (AIS)
AIS occurs when a person has XY chromosomes and internal testes, but their body partially or completely ignores testosterone. In the complete form, external anatomy looks typically female. The person has a vagina but no uterus, and the testes remain inside the abdomen. Pubic and underarm hair tends to be sparse or absent. Menstruation never begins, and the condition is often discovered only when a teenager is evaluated for not getting a period.
Partial androgen insensitivity falls on a spectrum. Some people have genitals that appear typically female, others typically male, and some have features of both. The degree depends on how much sensitivity to androgens the body retains.
Klinefelter Syndrome (47,XXY)
People with Klinefelter syndrome carry an extra X chromosome, giving them a total of 47 chromosomes instead of the usual 46. Physical traits can include taller-than-average height, long legs relative to the torso, a smaller penis, undescended testicles, flat feet, and coordination difficulties. During the teen years, some develop increased breast tissue. The testes often produce less testosterone and little to no sperm, which can affect fertility.
Swyer Syndrome
In Swyer syndrome, a person has XY chromosomes but develops a vagina, uterus, and fallopian tubes. Instead of functional ovaries or testes, they have streak gonads: small bands of nonfunctional tissue. This happens because the genes responsible for triggering testicular development, particularly the SRY gene in about 15 to 20 percent of cases, carry a mutation that prevents the testes from forming. Without testes producing testosterone, the body follows the default developmental pathway toward female anatomy. Swyer syndrome is typically discovered at puberty when menstruation doesn’t begin.
Gonadal Dysgenesis
Gonadal dysgenesis is a broader category where the gonads don’t develop normally. In its complete form, a person with XY chromosomes has female internal and external anatomy, sometimes with a slightly enlarged clitoris, and testosterone levels comparable to those found before puberty. Puberty doesn’t progress on its own. In the partial form, the picture is far more variable. Some people appear typically male at birth, others resemble Turner syndrome (a condition associated with a single X chromosome), and still others fall somewhere in between. Internal reproductive organs may be a mix of structures along the male and female developmental pathways. The gonads themselves can range from two malformed testes to one streak gonad paired with a partially formed testis.
When Intersex Traits Are Discovered
Some intersex conditions are obvious at birth. A baby may have genitals that doctors can’t immediately classify as male or female, prompting further evaluation. CAH in girls is often identified this way, especially in its classic form.
Other conditions remain hidden for years. Complete androgen insensitivity syndrome and Swyer syndrome commonly go unnoticed until adolescence, when a teenager doesn’t start menstruating or doesn’t develop expected secondary sex characteristics like breast growth or body hair changes. Klinefelter syndrome is sometimes caught in childhood due to developmental or coordination concerns, but many people aren’t diagnosed until adulthood when they’re being evaluated for infertility.
Still other variations are so subtle they’re never discovered at all. A person might carry an atypical chromosome pattern or have mild hormonal differences that never produce noticeable symptoms.
Terminology: Intersex vs. DSD
In medical literature, you’ll often see the term “differences of sex development” (DSD), which replaced the older “disorders of sex development” phrasing. The American Urological Association and several pediatric specialty groups use DSD as a clinical umbrella, while acknowledging that it’s an oversimplification for what is actually a wide range of distinct diagnoses. Many advocacy organizations and individuals prefer “intersex” because it’s more widely understood and carries less clinical stigma. Both terms refer to the same set of biological variations.
The Debate Over Early Surgery
For decades, the standard medical approach was to perform surgery on intersex infants to make their genitals appear more typically male or female. This practice has become one of the most contentious issues in intersex healthcare.
Multiple United Nations bodies have raised concerns. The UN Committee against Torture and the Special Rapporteur on torture have questioned the lack of informed consent for these procedures. The UN Special Rapporteur on health has recommended postponing non-emergency, irreversible interventions until the intersex person is old enough to participate in the decision. The European Parliament has gone further, issuing a resolution that “strongly condemns sex-normalising treatments and surgery.”
A handful of countries have acted on these recommendations. Malta, Portugal, and Germany have banned non-consensual, medically unnecessary surgeries on intersex children. India’s Tamil Nadu state did the same after a court ruled that parental consent cannot substitute for a child’s own consent. In the United States, only California has passed a resolution supporting the bodily autonomy of intersex youth, but it is nonbinding, and repeated attempts to pass enforceable legislation have failed. Throughout the Americas, from Brazil to Canada to Mexico, these surgeries without the patient’s informed consent remain standard practice.
The core concern is that surgery performed in infancy is irreversible, yet the child may grow up to identify differently than the sex they were assigned. Adults who underwent these procedures as infants have reported loss of sensation, psychological harm, and the need for additional surgeries. The growing medical and human rights consensus is shifting toward waiting, though practice on the ground has been slow to change.