Congenital adrenal hyperplasia (CAH) is a genetic condition where the adrenal glands can’t produce enough cortisol, causing the body to overproduce male sex hormones called androgens. In women and girls, this excess of androgens can affect everything from genital development at birth to menstrual cycles, body hair, and fertility later in life. About 90% to 95% of all CAH cases are caused by a specific enzyme deficiency that disrupts hormone production in the adrenal glands.
How CAH Disrupts Hormone Production
Your adrenal glands sit on top of your kidneys and produce cortisol, a hormone essential for managing stress, blood sugar, and blood pressure. To make cortisol, the adrenals need an enzyme called 21-hydroxylase. In CAH, mutations in the gene responsible for this enzyme (CYP21A2) mean the adrenals either can’t make this enzyme at all or make too little of it.
When cortisol production stalls, the brain detects the shortage and sends increasingly strong signals to the adrenal glands to work harder. This creates a feedback loop: the adrenals get flooded with stimulation but still can’t make cortisol. Instead, the raw materials that were supposed to become cortisol get rerouted into androgen production. The result is a body that’s low on cortisol and flooded with androgens, a combination that causes most of the symptoms women with CAH experience.
Classic vs. Nonclassic CAH
CAH exists on a spectrum, and the two main forms differ significantly in severity and when they’re detected.
Classic CAH
Classic CAH is the more severe form, found in about 1 in 15,000 births globally. It’s usually discovered at birth or in infancy. In the most severe subtype, called salt-wasting CAH, the adrenals produce almost no cortisol or aldosterone (a hormone that regulates salt and water balance). Without treatment, this can cause dangerously low blood pressure, low blood sugar, and a life-threatening adrenal crisis. In female infants, high androgen levels during fetal development can cause the external genitalia to appear atypical. The clitoris may be enlarged and resemble a penis, which is often the first sign that leads to diagnosis.
Nonclassic CAH
Nonclassic CAH is far more common, occurring in roughly 1 in 1,000 births worldwide, with some populations showing even higher rates. Among Caucasians, the estimated prevalence is about 1 in 200. This milder form doesn’t cause genital differences at birth and often goes undiagnosed until later childhood or adulthood. Many women with nonclassic CAH first seek answers when they develop irregular periods, excess body or facial hair, or difficulty getting pregnant. Because these symptoms overlap heavily with polycystic ovary syndrome (PCOS), nonclassic CAH is commonly misdiagnosed as PCOS.
Symptoms in Women and Girls
The androgen excess in CAH produces a recognizable pattern of symptoms in females, though the severity depends on whether the condition is classic or nonclassic.
- Excess hair growth: Facial hair, increased body hair, and sometimes a deeper voice result from elevated androgens.
- Menstrual irregularities: Periods may be irregular, infrequent, or absent entirely. This affects women with both classic and nonclassic forms.
- Early puberty: Children with CAH may develop pubic hair and other signs of puberty at an unusually young age. Rapid early growth followed by shorter adult height is common because excess androgens cause growth plates to close prematurely.
- Fertility challenges: Irregular ovulation makes conception harder, though with proper treatment, fertility rates are high.
- Genital differences at birth: This applies only to classic CAH, where prenatal androgen exposure affects external genital development.
How CAH Is Diagnosed
The key blood test for CAH measures a hormone precursor called 17-hydroxyprogesterone (17-OHP). In the normal hormone production pathway, 17-OHP gets converted into cortisol. When the enzyme is missing or deficient, 17-OHP builds up in the blood instead. For newborns, a heel-stick blood sample is collected 48 hours after birth, and a value above 5,000 ng/dL strongly points to classic CAH.
For older children and adults with suspected nonclassic CAH, a morning blood draw checks baseline 17-OHP levels. A result under a certain threshold effectively rules out CAH, while a very high result confirms it. When the result falls in an intermediate range, an ACTH stimulation test is the next step. This involves an injection that tells the adrenal glands to ramp up production, followed by a blood draw 60 minutes later. If 17-OHP levels spike above 30 nmol/L after stimulation, the diagnosis is confirmed. Genetic testing of the CYP21A2 gene can provide additional confirmation.
Telling CAH Apart From PCOS
Because nonclassic CAH and PCOS share so many symptoms, including irregular periods, excess hair growth, and elevated androgens, distinguishing between them requires specific testing. PCOS is diagnosed based on a combination of androgen excess, irregular periods, and the appearance of the ovaries on ultrasound, with at least two of these three criteria present. But the guidelines also require ruling out other conditions that mimic PCOS, and CAH is one of the most important to exclude.
The distinguishing test is the 17-OHP blood draw. Experts recommend that every woman being evaluated for PCOS receive this screening. Women with nonclassic CAH are also more likely than those with PCOS to have a history of early puberty, which can be a useful clinical clue. Getting the right diagnosis matters because the underlying cause, and therefore the treatment approach, is different.
Treatment and Daily Management
The cornerstone of CAH treatment is replacing the cortisol the body can’t make on its own. Taking a glucocorticoid medication serves two purposes: it provides the cortisol your body needs and signals the brain to stop overstimulating the adrenal glands, which in turn reduces androgen production. Women with the salt-wasting form of classic CAH also need a mineralocorticoid to replace aldosterone and maintain proper salt and fluid balance.
The central challenge of treatment is finding the right dose. Too little medication leaves androgens elevated, causing ongoing symptoms. Too much tips the balance toward glucocorticoid excess, which carries its own risks. Women with CAH need regular monitoring to keep this balance in check, typically through blood tests that track hormone levels alongside clinical assessment of symptoms.
During illness, injury, or surgery, the body normally produces a surge of cortisol to cope with the stress. Women with CAH can’t do this on their own and need to increase their medication dose during these situations to prevent an adrenal crisis. Many carry an emergency injection kit for situations where they can’t take oral medication.
Fertility and Pregnancy
Pregnancy is very achievable for most women with CAH. Recent studies show that women with classic CAH who want to become pregnant can reach fertility rates around 90%, only slightly below the general population. The key is adequate androgen suppression to allow regular ovulation.
When actively trying to conceive, women with CAH typically need higher doses of glucocorticoid medication than their usual maintenance dose. This more aggressive suppression of androgens helps restore a hormonal environment that supports ovulation and conception. For those who take longer to conceive, a reproductive endocrinologist can explore additional fertility treatments.
Once pregnant, managing CAH requires close coordination between an endocrinologist and an obstetrics team. Glucocorticoid doses may need to increase as the pregnancy progresses, and a clear plan for medication during labor and delivery is essential to prevent adrenal crisis during the physical stress of birth.
Long-Term Health Considerations
Living with CAH means taking glucocorticoid medication for life, and long-term steroid use carries real health trade-offs. One of the most significant is bone health. Glucocorticoid therapy is one of the leading causes of secondary osteoporosis, affecting an estimated 30% to 50% of people on chronic treatment. These medications accelerate bone breakdown in the early stages and impair new bone formation over time by reducing the number and function of bone-building cells.
There’s a partial counterbalance in women with CAH: excess androgens get converted to estrogen, which supports bone health. But if glucocorticoid doses are too high, they can suppress the reproductive hormone system, potentially reducing estrogen levels and removing that protective effect. This is another reason why dose optimization is so critical.
Cardiovascular health and metabolic changes are also areas of concern with long-term glucocorticoid use. Regular monitoring of bone density, blood pressure, blood sugar, and weight helps catch problems early, making ongoing follow-up with an endocrinologist an important part of living well with CAH.