Respiratory diseases range from common infections like the flu to chronic conditions like COPD and asthma, and they collectively represent one of the largest health burdens worldwide. In 2023 alone, chronic respiratory diseases accounted for roughly 569 million cases and 4.2 million deaths globally. Understanding the major categories helps you recognize symptoms early and know what to expect from each condition.
Asthma
Asthma is a chronic condition where the airways become inflamed, narrow, and overly sensitive to triggers. When an asthma episode strikes, the muscles around your airways tighten, the lining swells, and extra mucus clogs the passageways. This causes wheezing, chest tightness, coughing, and shortness of breath. Unlike many other respiratory diseases, the airflow obstruction in asthma is reversible, meaning symptoms can improve on their own or with treatment.
What sets asthma apart is how reactive the airways become. Even mild exposure to a trigger can set off a disproportionate response. Common triggers include pollen, dust mites, tobacco smoke, air pollution, respiratory viruses, and fungal spores. Some people develop asthma in childhood alongside allergies, while others develop it as adults in response to occupational irritants, infections, or pollution. Adult-onset asthma tends to be harder to control and sometimes doesn’t respond well to standard treatments.
Chronic Obstructive Pulmonary Disease (COPD)
COPD is an umbrella term for two conditions that usually occur together: chronic bronchitis and emphysema. Both cause permanent, progressive damage that makes breathing harder over time.
In chronic bronchitis, the tubes that carry air into your lungs (the bronchi) become inflamed and narrowed. The walls thicken, leaving less room for air to pass through, and the irritation triggers excess mucus production that clogs the already-narrowed passages. This leads to a persistent cough with mucus, often called a “smoker’s cough,” though nonsmokers can develop it too.
Emphysema attacks deeper in the lungs. The tiny air sacs where oxygen enters your bloodstream become damaged and eventually rupture, merging into fewer, larger spaces. This dramatically reduces the surface area available for gas exchange. The result is progressive breathlessness, first during exertion and eventually at rest. Once these air sacs are destroyed, they don’t grow back. Long-term smoking is the primary cause, though prolonged exposure to air pollution, chemical fumes, and dust also contributes.
Pneumonia
Pneumonia is an infection that fills the air sacs of one or both lungs with fluid or pus. It can be caused by bacteria, viruses, or (less commonly) fungi. The symptoms overlap regardless of the cause: chest pain when breathing or coughing, fever or chills, fatigue, shortness of breath, and sometimes nausea or confusion.
The most common bacterial culprits in community settings are Streptococcus pneumoniae and Mycoplasma pneumoniae. On the viral side, influenza, RSV, COVID-19, and several other respiratory viruses can all trigger pneumonia. Bacterial pneumonia tends to hit harder and faster, with high fever and productive cough, while viral pneumonia often develops more gradually. Fungal pneumonia is rarer and typically affects people with weakened immune systems. Severity ranges widely, from mild cases treatable at home to life-threatening infections requiring hospitalization, especially in young children, older adults, and people with other health conditions.
Tuberculosis
Tuberculosis (TB) is a bacterial infection that primarily targets the lungs, though it can spread to the kidneys, spine, and brain. The bacteria travel through the air when someone with active TB disease coughs, speaks, or sings. Transmission is far more likely in indoor spaces with poor ventilation than outdoors.
Not everyone who inhales TB bacteria gets sick. Many people carry a latent infection where the bacteria remain dormant and cause no symptoms. When TB does become active, it causes a persistent cough (often with blood), chest pain, weight loss, night sweats, and fever. Only active TB in the lungs or throat is contagious. Latent TB and TB in other body parts typically cannot spread to others. TB remains one of the leading infectious causes of death worldwide, particularly in regions with limited access to diagnosis and treatment.
Pulmonary Fibrosis
Pulmonary fibrosis belongs to a group called interstitial lung diseases, where the tissue between the air sacs becomes damaged and scarred. The scarring makes the lungs stiff and thick, which makes it increasingly difficult for oxygen to pass into the bloodstream. Breathing feels like trying to inflate a balloon that’s lost its stretch.
In idiopathic pulmonary fibrosis (IPF), the most common form, the scarring appears to result from a repeated cycle of damage and healing that eventually goes wrong. The healing process itself becomes dysfunctional, producing scar tissue instead of healthy lung tissue. What triggers this cycle in the first place remains unknown, though smoking is a well-established risk factor. Other forms of interstitial lung disease can be traced to specific causes: asbestos exposure, certain medications, autoimmune conditions, or inhaling organic dusts over long periods. The scarring is irreversible, so treatment focuses on slowing progression and managing symptoms.
Cystic Fibrosis
Cystic fibrosis (CF) is a genetic disease caused by mutations in the gene that produces a protein responsible for moving salt and water across cell surfaces. When this protein doesn’t work properly, the balance of salt and water in tissues throughout the body is disrupted. In the lungs, this dehydrates the thin layer of liquid that normally keeps airways moist and slippery.
The result is abnormally thick, sticky mucus that clogs small airways and creates a breeding ground for bacteria, particularly Pseudomonas aeruginosa. Chronic lung infections and progressive lung damage are the hallmarks of CF and the leading cause of reduced life expectancy. But CF isn’t limited to the lungs. It affects all tissues lined with the type of cells that rely on this protein, including the pancreas, liver, intestines, and reproductive organs. Newer therapies that target the defective protein itself have transformed outcomes for many people with CF, though the specific treatment depends on which genetic mutation a person carries.
Pulmonary Hypertension
Pulmonary hypertension is high blood pressure in the arteries that carry blood from the heart to the lungs. This forces the right side of the heart to pump harder, and over time it weakens. Symptoms include shortness of breath during activity, fatigue, chest pressure, and swelling in the ankles or legs.
There are five broad categories based on the underlying cause. Pulmonary arterial hypertension involves remodeling of the small arteries in the lungs, sometimes triggered by drugs like methamphetamines or linked to conditions like autoimmune disease, liver disease, or HIV. The second category stems from left heart disease, where problems on the left side of the heart back up pressure into the lungs. Chronic lung diseases like COPD and pulmonary fibrosis can also raise pulmonary pressure through a third pathway. A fourth type results from blood clots that chronically obstruct blood flow through the lungs. The fifth category captures cases with multiple contributing factors, including conditions like sickle cell disease and sarcoidosis.
How Lung Function Is Measured
Breathing tests called spirometry are used to diagnose and classify many respiratory diseases. The test measures two key values: how much air you can blow out in one second (FEV1) and the total amount you can forcefully exhale (FVC). In healthy lungs, the ratio of these two numbers is above 0.70, and both values fall above 80% of what’s predicted for your age, height, and sex.
When the ratio drops below 0.70, it signals an obstructive pattern, meaning something is blocking airflow out of the lungs. This is the pattern seen in asthma and COPD. The FEV1 value then grades severity: above 70% of predicted is mild, 60 to 69% is moderate, 50 to 59% is moderately severe, 35 to 49% is severe, and below 35% is very severe. A restrictive pattern, where the lungs can’t fully expand, shows up differently: the ratio stays normal or even increases, but total lung capacity drops. This pattern is typical of pulmonary fibrosis and other interstitial lung diseases.
Warning Signs of Respiratory Distress
Some breathing symptoms require immediate attention regardless of the underlying cause. A bluish tint around the mouth, inside the lips, or on the fingernails indicates oxygen levels have dropped dangerously low. The skin may also appear pale or gray. Visible retractions, where the skin pulls inward below the neck, under the breastbone, or between the ribs with each breath, signal that the body is straining to get air into the lungs. Nostrils that flare wide open during breathing are another sign of serious effort. Any combination of these signs warrants calling emergency services immediately.