Cystic fibrosis (CF) affects nearly every organ system in the body, though its most serious effects hit the lungs and digestive tract. The disease stems from a faulty protein that controls how chloride and water move through cells, leading to abnormally thick, sticky mucus that clogs airways, blocks digestive enzymes, and damages organs over time. For babies born with CF between 2020 and 2024, the predicted median survival age is now 65 years, a dramatic improvement from previous decades.
How CF Disrupts the Body at a Cellular Level
CF is caused by mutations in the gene responsible for building a protein channel that transports chloride ions into and out of cells. This chloride movement normally pulls water along with it, keeping the mucus that lines your airways, digestive organs, and reproductive tract thin and slippery. When the channel doesn’t work properly, water can’t flow to where it’s needed. The result is mucus that’s dehydrated, dense, and difficult for the body to clear. This single defect cascades into problems across multiple organ systems, each with its own set of complications.
Lung Damage and Chronic Infection
The lungs bear the heaviest burden. Thick mucus coats the airways and creates a warm, stagnant environment where bacteria thrive. In childhood, the most common infections come from Staphylococcus aureus and Haemophilus influenzae. As people with CF get older, a particularly stubborn bacterium called Pseudomonas aeruginosa often takes hold and becomes the dominant infection in roughly half of adults. The airways also harbor a complex mix of other microbes, many of which seed from the mouth into the lower respiratory tract.
These infections aren’t one-time events. They become chronic, triggering ongoing inflammation that gradually scars and destroys lung tissue. Over years, this cycle of infection and inflammation erodes lung function, with the steepest declines happening during acute flare-ups called pulmonary exacerbations. Respiratory failure remains the leading cause of death in people with CF.
Digestive Problems and Nutritional Gaps
About 85% of people with CF have pancreatic insufficiency, meaning their pancreas can’t deliver enough digestive enzymes to the small intestine. The same thick mucus that clogs the lungs also blocks the tiny ducts of the pancreas, preventing enzymes from reaching food as it passes through the gut. Without these enzymes, the body struggles to break down and absorb fats and fat-soluble vitamins (A, D, E, and K). This leads to greasy, bulky stools, poor weight gain, and nutritional deficiencies that can affect growth in children and overall health at any age.
People with pancreatic insufficiency take enzyme replacement capsules with every meal and snack to compensate. Even with enzyme therapy, absorbing enough calories and nutrients requires careful attention to diet. Many people with CF need to eat significantly more calories than average just to maintain a healthy weight.
CF-Related Diabetes
As pancreatic damage accumulates over time, the insulin-producing cells in the pancreas can also be affected. CF-related diabetes (CFRD) is distinct from both type 1 and type 2 diabetes, though it shares features of each. It’s relatively rare in young children (about 2%) but becomes increasingly common with age: roughly 19% of adolescents and 40 to 50% of adults with CF develop it. Screening typically begins around age 6 with annual glucose tolerance testing.
CFRD matters because uncontrolled blood sugar accelerates lung function decline and worsens nutritional status. Managing it usually involves insulin, since the core problem is that the damaged pancreas can no longer produce enough.
Liver Disease
Thick secretions can also block the bile ducts in the liver, leading to CF-related liver disease. A large French study found that about 18% of patients had liver involvement at the time they were evaluated, with the incidence climbing roughly 1% per year from birth and reaching about 32% by age 25 before leveling off. Most cases involve an enlarged liver, abnormal liver function tests, or changes visible on ultrasound. Severe liver disease, including significant scarring and complications from increased pressure in the liver’s blood vessels, develops in around 5% of patients.
Bone Health
People with CF are at substantially higher risk for weak bones. Poor absorption of vitamin D and calcium, chronic inflammation, reduced physical activity during illness, and certain medications all contribute. National registries in the U.S., France, and the U.K. report that about 25% of adults with CF have lower-than-expected bone density, but more detailed single-center studies suggest the true number may be closer to 50%. Weakened bones increase fracture risk, which can further limit the ability to exercise and do airway clearance treatments.
Effects on Fertility
CF has a pronounced effect on male fertility. Between 97 and 98% of men with CF are infertile because the vas deferens, the tube that carries sperm from the testicles, never develops. Sperm production itself is normal in about 90% of these men, but the sperm have no path to reach the semen. Sexual function is unaffected, and biological fatherhood is possible through assisted reproductive techniques that retrieve sperm directly from the testicles.
Women with CF can conceive naturally, though thicker cervical mucus may reduce fertility somewhat. Pregnancy is increasingly common as life expectancy improves, though it requires close monitoring because of the additional demands on lung function and nutrition.
The Daily Treatment Burden
Living with CF means managing a demanding daily routine. The average adult with CF spends 1.5 to 2 hours each day on treatments alone. This typically includes airway clearance therapy (techniques or devices that loosen and help expel mucus from the lungs), inhaled medications delivered through a nebulizer, and enzyme capsules taken with every meal. Many people also take inhaled antibiotics, anti-inflammatory drugs, vitamins, and, if they have CFRD, insulin.
The introduction of highly effective modulator therapies, drugs that partially fix the underlying protein defect, has transformed outcomes for many people with CF over the past decade. These medications can significantly improve lung function, reduce pulmonary flare-ups, and improve weight gain. They’re a major reason the predicted survival age has climbed so sharply. Still, modulators don’t work for every CF mutation, and most people continue some version of their daily treatment routine even when on these newer drugs.
How CF Is Diagnosed
Most cases are now caught through newborn screening. When screening flags a potential case, a sweat test confirms or rules out the diagnosis. The test measures chloride concentration in sweat, since the same faulty channel that dehydrates mucus also causes unusually salty sweat. A sweat chloride level of 60 mmol/L or higher confirms CF. Levels below 30 mmol/L make CF unlikely. Results between 30 and 59 mmol/L fall into an intermediate range that requires further genetic testing to clarify.