Cystic fibrosis (CF) causes thick, sticky mucus to build up in the lungs, pancreas, and other organs, producing symptoms that typically fall into two categories: respiratory and digestive. Most people are diagnosed in infancy through newborn screening, but the severity and combination of symptoms varies widely from person to person. Some people experience serious lung problems early in life, while others have milder symptoms that go undetected until adulthood.
Why CF Produces So Many Different Symptoms
CF is caused by mutations in a gene that controls a protein responsible for moving chloride (a component of salt) in and out of cells. That chloride movement normally pulls water along with it, keeping the mucus that lines your lungs, digestive tract, and other organs thin and slippery. When the protein doesn’t work correctly, water can’t flow properly, and the mucus becomes abnormally thick. This single defect creates problems in every organ that relies on mucus to function, which is why CF affects so many different parts of the body at once.
Lung and Respiratory Symptoms
The lungs take the hardest hit. Thick mucus clogs the airways, trapping bacteria and making infections difficult to clear. The hallmark respiratory symptoms include a persistent cough that produces mucus (sometimes streaked with blood), wheezing, and frequent lung infections. Over time, repeated infections and inflammation damage the airways, gradually widening them and reducing lung function.
Flare-ups, called pulmonary exacerbations, bring a noticeable worsening of these baseline symptoms. You might cough more, feel increased chest congestion, and notice a change in mucus color. Sinus infections are also common and can become chronic, sometimes accompanied by nasal polyps, which are soft growths inside the nasal passages.
CF is progressive, meaning lung damage accumulates over time. A child might start with occasional coughing and mild wheezing, then develop more frequent infections and declining lung capacity through adolescence and adulthood. How quickly this happens depends on the specific genetic mutation, treatment, and individual factors that vary considerably from one person to the next.
Digestive and Nutritional Symptoms
The same thick mucus that clogs the lungs also blocks the tubes that carry digestive enzymes from the pancreas to the small intestine. Without those enzymes, the intestines can’t properly break down and absorb nutrients from food. This creates a distinctive set of digestive symptoms:
- Greasy, foul-smelling stools caused by undigested fat passing through the body
- Poor weight gain and growth despite a normal or even large appetite
- Chronic or severe constipation, sometimes with frequent straining that can cause part of the rectum to protrude from the anus
- Intestinal blockages, which can occur at any age
In newborns, the very first sign of CF is sometimes a condition called meconium ileus, where abnormally thick first stool blocks the intestine and requires medical intervention. This occurs in roughly 15 to 20 percent of babies born with CF and is often what prompts the initial diagnosis.
The malabsorption problem means that children with CF may be noticeably smaller than their peers, even if they eat plenty of food. Adults can struggle with unintended weight loss. Nutritional deficiencies in fat-soluble vitamins (A, D, E, and K) are common because those vitamins depend on fat absorption to enter the body.
CF-Related Diabetes
As thick mucus damages the pancreas over time, it can impair the organ’s ability to produce insulin. Nearly 30 percent of adults with CF develop CF-related diabetes, and that figure climbs above 40 percent for adults between ages 50 and 60. This form of diabetes is distinct from both Type 1 and Type 2, though it shares features with each.
The tricky part is that many of its symptoms overlap with CF itself: fatigue, difficulty gaining weight, increased thirst, and frequent urination. An unexplained drop in lung function or a rise in infections can also signal the onset of CF-related diabetes. Because the symptoms blend so easily with existing CF issues, routine screening is typically part of ongoing CF care starting in the teen years.
Symptoms in Infants and Young Children
All 50 U.S. states screen newborns for CF using a blood test that measures a pancreatic enzyme. A positive screen is followed by a sweat test, which measures how much chloride is in sweat. A chloride level of 60 millimoles per liter or higher confirms a CF diagnosis, while a level under 30 makes CF unlikely. Values between 30 and 59 fall in an intermediate range that requires further evaluation.
Even before test results come back, certain signs can point to CF in newborns and infants. Meconium ileus is the most dramatic early presentation. Other early signs include salty-tasting skin (parents sometimes notice this when kissing their baby), failure to gain weight, frequent greasy stools, and recurrent respiratory infections. Some infants develop a persistent cough within their first months of life.
Late Diagnosis and Atypical Symptoms
Not everyone with CF fits the classic picture. Atypical CF is a milder form that may affect only one organ or produce symptoms that come and go. People with this form are often diagnosed as older children, teenagers, or even adults because their symptoms never seemed severe enough to raise a red flag.
The symptoms that eventually lead to a late diagnosis can look quite different from classic CF. Chronic sinus problems, recurring bouts of pancreatitis, persistent diarrhea, and unexplained weight loss are common presentations. Some people experience episodes of dehydration or heat-related illness caused by abnormal electrolyte levels in their sweat. Fertility issues, particularly in men, can also be the first recognized sign. About 98 percent of men with CF are infertile due to a missing or blocked reproductive duct, and this is sometimes discovered only during fertility evaluations.
Because atypical CF can fly under the radar for years, adults who have dealt with unexplained chronic sinusitis, recurrent lung infections, or digestive problems that don’t respond to standard treatments may benefit from being evaluated for CF, even if they were never flagged on a newborn screen.