Cystic fibrosis (CF) is a genetic disease that causes the body to produce abnormally thick, sticky mucus, leading to serious problems in the lungs, digestive system, and other organs. About 1 in 2,500 newborns in the United States is born with it, making it the most common life-threatening inherited disease in white populations. Thanks to major treatment advances, the predicted median survival age for someone born with CF today is 65 years, a dramatic improvement from just a few decades ago.
How CF Works in the Body
Every cell that produces mucus, sweat, saliva, tears, or digestive enzymes relies on a protein channel that moves chloride (a component of salt) in and out of cells. This chloride movement controls how water flows through tissues, and that water is what keeps mucus thin and slippery.
In cystic fibrosis, the gene responsible for building that channel is faulty. The result: chloride can’t move properly, water doesn’t follow, and the mucus lining the lungs, pancreas, and other organs becomes dehydrated and glue-like. That thick mucus traps bacteria, blocks ducts, and triggers chronic inflammation throughout the body.
How CF Is Inherited
CF follows an autosomal recessive pattern, meaning a child must inherit one defective copy of the CFTR gene from each parent to develop the disease. If both parents are carriers (they each have one faulty copy and one working copy), every pregnancy carries a 25% chance the child will have CF, a 50% chance the child will be a carrier without symptoms, and a 25% chance the child won’t carry the mutation at all.
Over 1,500 unique mutations in the CFTR gene have been identified. The most common one, called F508del, accounts for more than 66% of CF-causing genes in people of European descent. Which mutations a person carries influences how severe their disease is and which treatments work best.
Effects on the Lungs
Lung disease is the primary driver of illness and shortened lifespan in CF. The thick mucus coating the airways creates an ideal environment for bacteria to thrive, leading to repeated infections that gradually scar and damage lung tissue. Over time, this cycle of infection and inflammation reduces the lungs’ ability to move air efficiently.
Poor nutrition from digestive problems compounds the lung damage. When the body can’t absorb enough calories and nutrients, respiratory muscles (including the diaphragm and the muscles between the ribs) weaken, and immune defenses falter. This creates a feedback loop where nutritional decline and lung decline accelerate each other.
Effects on Digestion
The pancreas is one of the organs hit earliest and hardest. Thick secretions block the ducts that deliver digestive enzymes to the small intestine, meaning food, especially fats and fat-soluble vitamins, passes through without being properly broken down. This leads to malnutrition, poor growth in children, and greasy, bulky stools.
The pancreatic blockages start with abnormal enzyme secretions and progress over time as mucus accumulates in the ducts. The pancreas also fails to release enough bicarbonate, a substance that neutralizes stomach acid as food enters the intestine. Without it, the intestinal environment becomes too acidic for digestive enzymes to activate properly, and bile acids can precipitate out of solution, sometimes causing intestinal blockages.
About 15 to 20% of babies with CF develop meconium ileus, a bowel obstruction that occurs shortly after birth. A similar type of obstruction, called distal intestinal obstruction syndrome, can happen at any age.
CF-Related Diabetes
As pancreatic damage accumulates over years, the organ’s ability to produce insulin declines. Nearly 30% of adults with CF develop CF-related diabetes (CFRD), and that number climbs above 40% for adults between ages 50 and 60. CFRD shares features with both type 1 and type 2 diabetes: the pancreas doesn’t make enough insulin (like type 1), and the body’s cells can also become resistant to the insulin that is produced (like type 2).
High blood sugar levels in the airways can directly worsen lung infections by feeding bacterial growth. Insulin deficiency also pushes the body into a breakdown state that accelerates muscle wasting and weakens immunity, making CFRD a particularly dangerous complication.
How CF Is Diagnosed
In the United States, CF is typically caught through newborn screening. A few drops of blood from a baby’s heel are tested for elevated levels of a substance called immunoreactive trypsinogen (IRT), which is produced by the pancreas and runs high in newborns with CF. If IRT is elevated, a second test on the same blood sample looks for mutations in the CFTR gene. Babies who show both high IRT and at least one gene change are referred for further evaluation.
The gold standard for confirming CF is the sweat test, which measures how much chloride is in a person’s sweat. A chloride level of 60 mmol/L or higher confirms the diagnosis. Levels below 30 mmol/L make CF unlikely, and results between 30 and 59 mmol/L are considered borderline, requiring repeat testing or genetic analysis to reach a definitive answer.
Daily Treatment Routine
Living with CF means committing to a time-intensive daily care routine, often taking two to four hours. One of the cornerstones is airway clearance therapy, which physically loosens the thick mucus so it can be coughed out. The most common method uses an inflatable vest that rapidly vibrates the chest wall at high frequency, typically for about 20 minutes per session. Before these devices existed, someone else had to clap on the patient’s chest and back by hand. The vest lets people do the therapy independently.
Inhaled medications, including mucus-thinning drugs and antibiotics, are usually paired with airway clearance sessions. Because the pancreas can’t deliver digestive enzymes on its own, most people with CF take enzyme replacement capsules with every meal and snack to absorb enough nutrition. High-calorie diets are standard because the body burns extra energy fighting infections and working harder to breathe.
CFTR Modulator Therapies
The biggest treatment breakthrough in CF history has been a class of drugs called CFTR modulators, which target the root cause of the disease rather than just managing symptoms. These medications work directly on the faulty protein, helping it reach the cell surface and function more effectively as a chloride channel.
Four modulator therapies have been approved by the FDA: ivacaftor (Kalydeco), lumacaftor/ivacaftor (Orkambi), tezacaftor/ivacaftor (Symdeko), and the triple combination elexacaftor/tezacaftor/ivacaftor (Trikafta). Trikafta, approved in 2019, has been transformative because it targets the F508del mutation carried by the vast majority of people with CF. For many patients, it dramatically improves lung function, reduces hospitalizations, and improves quality of life in ways that were unimaginable a generation ago. These drugs are taken as daily oral pills, and while they don’t cure CF, they represent a fundamental shift from symptom management to treating the underlying protein defect.
Reproductive Impact
CF affects fertility differently in men and women. Nearly all men with CF are infertile because the thick secretions block or cause the absence of the tubes that carry sperm, though sperm production itself is usually normal and assisted reproduction is often successful. Women with CF can conceive naturally, though thicker cervical mucus may reduce fertility. With improving health outcomes, pregnancy has become increasingly common and generally safe for women whose lung function is stable.