Androgen insensitivity syndrome (AIS) is a condition where a person is born with XY chromosomes but their body cannot fully respond to androgens, the hormones typically responsible for male sexual development. This means the body produces testosterone normally, but the cells can’t use it. The result is that physical development follows a partially or fully female pattern despite male-typical genetics. It affects roughly 1 in 20,400 babies born with XY chromosomes.
How AIS Works at the Cellular Level
During fetal development, androgens like testosterone signal the body to develop male physical traits. These signals work through androgen receptors, proteins on the surface of cells that act like a lock waiting for a key. In AIS, a mutation in the gene that codes for this receptor (located on the X chromosome) means the lock is damaged. Testosterone is produced normally by the testes, but when it arrives at the cell, nothing happens, or very little does.
What’s particularly interesting is that the body still has functioning aromatase, an enzyme that converts testosterone into estrogen. This conversion happens in the testes themselves and in other tissues throughout the body, and it doesn’t require a working androgen receptor. So a person with AIS may have high testosterone levels that the body ignores while simultaneously responding to estrogen created from that same testosterone. This is why individuals with the complete form develop breasts and other female secondary sex characteristics at puberty.
The Three Forms of AIS
AIS exists on a spectrum, and the degree of androgen resistance determines which form a person has.
Complete AIS (CAIS)
In complete androgen insensitivity syndrome, the body doesn’t respond to androgens at all. External genitalia appear typically female, and most individuals are raised as girls with a female gender identity. Internally, however, there are no ovaries, fallopian tubes, or uterus. Instead, undescended testes sit in the pelvis or abdomen. Many people with CAIS don’t learn about their condition until puberty, when menstruation never arrives. Other signs include taller-than-average stature for a female, a shorter or narrower vagina, and sparse or absent pubic and underarm hair. About 1 in 20,000 genetically male infants are born with CAIS, making it the most common form.
Partial AIS (PAIS)
In partial androgen insensitivity syndrome, the body responds to some androgens but not others, or responds weakly. This creates a wide range of physical presentations. Some individuals have genitalia that appear typically female, some have genitalia that appear typically male, and others have features of both. Physical signs can include an enlarged clitoris, a small penis, a split scrotum, breast development in someone otherwise male-presenting, or partially undescended testes. PAIS is rarer, occurring in roughly 1 in 99,000 genetically male births. People with PAIS may identify as male, female, or both, and sex assignment at birth can vary.
Mild AIS (MAIS)
In mild androgen insensitivity syndrome, genitalia appear typically male and the condition may go unnoticed until adulthood. The primary issues are infertility and sometimes breast enlargement at puberty. Some experts classify MAIS as a subset of partial AIS rather than a separate category.
How AIS Is Diagnosed
Diagnosis often happens at different life stages depending on the form. CAIS is frequently discovered during childhood when a hernia repair reveals testes in the inguinal canal, or during adolescence when a teenager doesn’t get her period. PAIS is more likely to be identified at birth when genital appearance doesn’t fit typical male or female patterns. MAIS sometimes isn’t caught until a person seeks help for infertility.
The diagnostic process typically involves chromosomal analysis confirming an XY karyotype, which can be done through standard blood tests or more targeted techniques that look specifically for the Y chromosome. Hormone levels are measured to confirm that the testes are producing testosterone normally, which helps rule out other conditions where testosterone production itself is the problem. A pelvic ultrasound checks for the presence or absence of internal reproductive structures. If a uterus or fallopian tubes are found, AIS is essentially ruled out, since the anti-Müllerian hormone produced by testes prevents those structures from forming regardless of androgen sensitivity.
Genetic testing for mutations in the androgen receptor gene is commercially available and can detect the specific mutation in up to 95% of cases.
Puberty With AIS
For individuals with CAIS, puberty can feel surprisingly normal in many ways, just incomplete. The testes produce testosterone, and aromatase converts a portion of it into estrogen. Research published in the Journal of Clinical Endocrinology & Metabolism confirmed that pubertal growth and breast development in women with CAIS are driven by this estrogen, both from the testes directly and from conversion of androgens in other tissues. Breasts develop, growth spurts occur, and body fat redistributes in a female pattern. What doesn’t happen is menstruation (there’s no uterus) and there’s typically very little body hair, since hair growth in those areas depends on working androgen receptors.
For those with PAIS, puberty is less predictable. Depending on how much androgen sensitivity exists, a person might experience some combination of breast development and virilization, which can be distressing and often requires medical support to manage.
Management and Ongoing Care
There is no way to make androgen receptors work if they’re mutated, so management focuses on supporting physical health, hormonal balance, and emotional well-being.
Gonad Removal and Its Timing
Historically, the standard approach has been to remove the undescended testes to prevent a small risk of malignant changes. The timing of this surgery is debated. Removing the testes before puberty means a person will need hormone replacement to go through puberty at all. Leaving them in place allows puberty to happen naturally through the body’s own estrogen production, with removal afterward. Since most tumors found in undescended testes occur after puberty, many clinicians now favor delaying removal to allow spontaneous pubertal development.
After gonad removal, estrogen replacement therapy becomes necessary and is typically lifelong. Treatment usually starts with a low dose that gradually increases to adult levels. Because there is no uterus, progesterone is generally not added, though this has been debated. Recent analyses suggest progesterone offers little additional benefit for individuals without a uterus.
For people with PAIS who have a male gender identity, testosterone or its derivatives may be used instead, depending on their degree of androgen sensitivity.
Bone Health
One of the most significant long-term health concerns with AIS is reduced bone mineral density. The risk of osteopenia and osteoporosis is elevated, particularly in individuals who had their gonads removed early. Notably, lower bone density has been observed even before gonad removal, suggesting that androgen insensitivity itself plays a role in bone health independent of surgical timing. Fracture risk is higher than in the general population, making bone density monitoring an important part of long-term care.
Fertility
Individuals with CAIS are infertile. There are no ovaries to produce eggs, no uterus to carry a pregnancy, and the testes do not produce viable sperm. For those with mild or partial AIS who have some degree of testicular function, assisted reproductive technology has occasionally made biological fatherhood possible, though this remains uncommon.
The Psychological Side
Learning about AIS can be profoundly disorienting, whether the diagnosis comes in childhood, adolescence, or adulthood. Feelings of isolation are common. Many people describe a sense of being “the only one,” and the condition touches on deeply personal aspects of identity, body image, and sexuality.
Psychological support is considered one of the most important aspects of care from the patient’s perspective. Peer support through organizations like the AIS Support Group (AISSG) gives individuals and families access to medical information and personal accounts from others living with the condition. For many people, connecting with others who share their experience reduces the sense of isolation more effectively than clinical counseling alone, though both have value. Mental health support that addresses body image, disclosure decisions, grief around infertility, and identity questions is a core part of comprehensive AIS care.