What Is Cystic Fibrosis? What Causes It?

More than 30,000 people in the U.S. live with cystic fibrosis (CF.) Doctors diagnose about 1,000 new cases each year.

CF affects the cells in your body that make mucus, sweat, and digestive fluids. Normally, these are very thin and slippery to keep systems in your body running smoothly. But if you have CF, they become thick and glue-like. This blocks tubes and ducts throughout your body.

Over time, mucus builds up inside your airways. This makes breathing a struggle. The mucus traps germs and leads to infections. It can also cause severe lung damage like cysts (fluid-filled sacs) and fibrosis (scar tissue). That’s how CF got its name.

What Causes Cystic Fibrosis?

It’s not contagious. It’s caused by a change, or mutation, in a single gene called the cystic fibrosis transmembrane conductance regulator (CFTR.) This controls the flow of salt and fluids in and out of your cells. If the CFTR gene doesn’t work the way it should, a sticky mucus builds up throughout your body.

To get CF, you have to inherit a mutated copy of the gene from both your parents.

If you inherit only one, you won’t have any symptoms. But you’ll be a “carrier” of the disease. That means there’s a chance you could pass it on to your own children one day.

About 10 million Americans are CF carriers. Every time two CF carriers have a baby, there’s a 25% (1 in 4) chance that their baby will be born with CF.

Which Parts of the Body Does CF Affect?

The lungs aren’t the only part of the body that’s harmed by CF. The disease also affects the following organs:

Pancreas. The thick mucus caused by CF blocks ducts in your pancreas. This stops digestive enzymes (proteins that break down your food) from reaching your intestine. As a result, your body has a hard time absorbing the nutrients it needs. Over time, this can also lead to diabetes.

Liver. If the tubes that remove bile become clogged, your liver gets inflamed and severe scarring called cirrhosis happens.


Small intestine. Because breaking down high-acid foods that come from the stomach is a challenge, the lining of the small intestine can erode.

Large intestine. Thick secretions in your stomach can make your feces (your poop) very thick. This can cause blockages. In some cases, the intestine may also start to fold in on itself like an accordion, called “intussusception.”

Bladder. Chronic coughing weakens the bladder muscles. Almost 65% of women with CF have stress incontinence. This means that you leak urine when you cough, sneeze, laugh, or lift something. Though more common in women, men can have it, too.

Kidneys. Some people with CF get kidney stones. These small, hard mineral deposits can cause nausea, vomiting, and pain. If ignored, they can lead to a kidney infection.

Reproductive organs. Excess mucus affects fertility in men and women. Most men with CF have problems with the tubes that transport their sperm, called the vasa deferentia. Women with CF have very thick cervical mucus, which can make it harder for a sperm to fertilize an egg.

Other parts of the body. CF can also lead to muscle weakness and to a thinning of the bones, called osteoporosis.  Because it upsets the balance of minerals in the blood, it can also bring about low blood pressure, fatigue, a fast heart rate, and a general feeling of weakness.

Although CF is a severe condition that needs daily care, many treatments for it have improved. People who have CF live much longer than they used to, and their quality of life has improved as well.

WebMD Medical Reference Reviewed by Hansa D. Bhargava, MD on March 26, 2019



Cystic Fibrosis Foundation: “About Cystic Fibrosis,” “CF Genetics: The Basics.”

American Lung Foundation: “Learn about Cystic Fibrosis,” “Cystic Fibrosis,” “Fertility in Women with CF.”

National Human Genome Research Institute: “Learning about Cystic Fibrosis.”

Mayo Clinic: “Cystic Fibrosis.”

YourGenome.org: “What is cystic fibrosis?”

National Center for Advancing Translational Sciences/Genetic and Rare Diseases Information Center: “Cystic fibrosis.”

The Childhood Liver Disease Research Network: “Cystic Fibrosis Liver Disease.”

Johns Hopkins Cystic Fibrosis Center: “Effects of CF: Pancreas/Gastrointestinal Tract: Intestinal Problems,” “Effects of CF: Muscle/Bone,” “Effects of CF: Reproduction,” “Effects of CF: Bladder/Kidney.”

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