Congenital adrenal hyperplasia (CAH) is a group of inherited conditions where the adrenal glands can’t produce certain hormones normally. The most common form, responsible for about 95% of cases, involves a missing enzyme that the adrenal glands need to make cortisol (the body’s stress hormone) and aldosterone (which regulates salt and water balance). Without this enzyme, the raw materials that would normally become cortisol and aldosterone get rerouted into androgens, or male sex hormones, causing a cascade of problems that can range from life-threatening in infancy to subtle enough to go unnoticed until adulthood.
How CAH Disrupts Hormone Production
Your adrenal glands sit on top of your kidneys and produce hormones your body depends on every day. To make cortisol and aldosterone, the adrenals need an enzyme called 21-hydroxylase. In CAH, a genetic mutation means the body produces too little of this enzyme, or none at all. The hormone-building process stalls partway through, and the partially built molecules pile up. The adrenal glands convert these leftover molecules into androgens instead.
The result is a double problem: too little cortisol and aldosterone, and too much androgen. Cortisol helps the body respond to illness, injury, and physical stress. Aldosterone keeps sodium and potassium in balance. Androgens drive the development of typically male physical traits. When androgen levels spike during fetal development, they can alter how a baby’s body forms before birth. After birth, the ongoing hormone imbalance affects growth, puberty, and overall health if left untreated.
Classic vs. Non-Classic CAH
CAH falls into two broad categories based on how much enzyme activity remains.
Classic CAH is the more severe form, found in about 1 in 15,000 births worldwide. It’s usually discovered at birth or in infancy because the enzyme deficiency is near-total. People with classic CAH have a severe lack of cortisol production, and most also have reduced aldosterone. Classic CAH itself has two subtypes. In the salt-wasting form (the more common of the two), aldosterone production drops so low that the body can’t retain enough sodium. Newborns can become dangerously dehydrated within the first few weeks of life if the condition isn’t caught quickly. In the simple virilizing form, the body still makes enough aldosterone to maintain salt balance, but androgen levels are still elevated enough to cause physical changes.
Non-classic CAH is far more common, occurring in roughly 1 in 1,000 births. It’s much milder because the enzyme still works partially. Many people with non-classic CAH aren’t diagnosed until later in childhood or adulthood, when symptoms like early pubic hair, persistent acne, or irregular periods prompt testing.
Signs in Newborns and Infants
The most visible sign of classic CAH at birth appears in female infants. Excess androgens during fetal development can cause the external genitalia to look atypically masculine. The clitoris may be enlarged and resemble a penis, and the labia may be partly fused, resembling a scrotum. In some cases, the urinary opening and vaginal opening merge into a single channel. Internally, the reproductive organs (uterus, ovaries, fallopian tubes) develop normally.
Male infants with classic CAH typically look normal at birth, which makes diagnosis trickier. Without newborn screening, boys with the salt-wasting form may not be identified until they develop a salt-losing crisis in the first few weeks of life, showing signs like vomiting, dehydration, and poor feeding. This is one reason newborn screening programs are so important for catching CAH early in all babies regardless of sex.
Symptoms in Children and Adults
Both boys and girls with CAH can develop early pubic hair, acne, and a rapid growth spurt during childhood. While they may be tall for their age initially, the early bone maturation that comes with excess androgens causes the growth plates to close sooner, often resulting in a shorter final adult height than expected.
Teenage and adult women with CAH, particularly the non-classic form, may experience irregular or absent menstrual periods, excess facial and body hair, a deepening voice, and difficulty with fertility. Men with CAH can also face fertility challenges. Non-classic CAH sometimes goes undiagnosed for years because its symptoms overlap with other hormonal conditions like polycystic ovary syndrome.
How CAH Is Inherited
CAH follows an autosomal recessive inheritance pattern, meaning a child must inherit one copy of the affected gene from each parent to develop the condition. Parents who each carry one copy are called carriers. They typically have no symptoms themselves. When two carriers have a child, there’s a 25% chance with each pregnancy that the child will have CAH, a 50% chance the child will be a carrier, and a 25% chance the child will neither have the condition nor carry it.
Newborn Screening and Diagnosis
Most countries with newborn screening programs test for classic CAH using a blood sample taken from a heel prick about 48 hours after birth. The test measures levels of 17-hydroxyprogesterone (17-OHP), one of those intermediate molecules that builds up when the 21-hydroxylase enzyme is missing. A very high reading flags the baby for follow-up testing, which usually includes additional blood work to confirm the diagnosis and determine the specific type.
Non-classic CAH isn’t reliably caught by newborn screening because 17-OHP levels are only mildly elevated. It’s usually diagnosed later when symptoms appear, through a blood test that measures 17-OHP either at baseline or after a stimulation test that challenges the adrenal glands to reveal whether they’re functioning properly.
Treatment and Daily Management
The cornerstone of CAH treatment is replacing the hormones the body can’t make on its own. For cortisol replacement, hydrocortisone is the preferred medication in children because longer-acting alternatives carry a higher risk of suppressing growth. It’s typically taken three times a day to mimic the body’s natural rhythm of cortisol release. Adults may switch to longer-acting options that only need to be taken once or twice daily.
Children and adults with the salt-wasting form also take a medication that replaces aldosterone, helping the body hold onto sodium and maintain fluid balance. Infants with salt-wasting CAH often need salt supplements as well, since breast milk and formula alone may not provide enough sodium.
Doctors adjust medication doses over time based on blood tests that track the levels of those intermediate hormones. The goal is a careful balance: enough medication to suppress excess androgen production and prevent symptoms, but not so much that the side effects of the medication itself (like slowed growth or weight gain) become a problem.
Stress Dosing and Adrenal Crisis
Because people with classic CAH can’t ramp up their own cortisol production when the body is under stress, they need to increase their medication dose during illness, injury, or surgery. This practice, called stress dosing, prevents a potentially life-threatening adrenal crisis, where cortisol levels drop so low that blood pressure plummets and the body can go into shock.
People with CAH and their families learn to recognize early warning signs of crisis (nausea, vomiting, extreme fatigue, dizziness) and carry emergency supplies. Many also wear medical alert identification so that first responders know to administer treatment quickly if they’re found unconscious. Living with CAH means building stress dosing into an automatic routine whenever illness strikes, much like a person with severe allergies keeps an epinephrine injector on hand.
Long-Term Outlook
With consistent treatment, most people with CAH live full, healthy lives. Fertility can be affected in both men and women, but many people with CAH do have children, sometimes with the help of reproductive specialists. Female infants born with atypical genitalia may undergo reconstructive surgery, though the timing and approach to surgery has become a more individualized decision in recent years.
Growth management during childhood is one of the trickier aspects of treatment. Because both the excess androgens and the glucocorticoid medications used to treat them can affect growth, pediatric endocrinologists monitor height, bone age, and hormone levels closely throughout childhood to keep both in check. Non-classic CAH generally requires less intensive management, and some people with very mild forms may not need daily medication at all, only treatment during specific situations like pregnancy planning.