A lung infection is an infection in any part of the respiratory system below the throat, where a virus, bacterium, or fungus triggers inflammation that disrupts normal breathing. These infections range from mild bronchitis that clears on its own to severe pneumonia that can be life-threatening. In 2023, lower respiratory infections were responsible for an estimated 2.5 million deaths worldwide, with children under 5 and adults over 70 carrying the highest burden.
Where the Infection Occurs Matters
The term “lung infection” covers several conditions, and the key difference between them is location. Bronchitis infects the bronchial tubes, the airways that run from your windpipe into your lungs. The main symptom is a persistent cough, often producing yellow-green mucus, along with a sore throat, mild fever, body aches, and fatigue. Acute bronchitis typically lasts 10 to 14 days, with some symptoms lingering up to three weeks.
Pneumonia is deeper and more serious. It infects the alveoli, the tiny air sacs at the very ends of your airways that transfer oxygen into your bloodstream. When those sacs fill with fluid, inflammatory cells, and debris, your body struggles to get the oxygen it needs. That’s why pneumonia produces more severe, whole-body symptoms: high fever (sometimes reaching 105°F), chills, sweating, shortness of breath, chest pain when coughing, confusion, and loss of appetite. A cough can persist for weeks even after the infection itself resolves.
Bronchiolitis affects the smallest airways (bronchioles) and is most common in infants and toddlers. The lining of these tiny passages swells, and thick plugs of cell debris can partially block airflow, trapping air in the lungs.
What Causes Lung Infections
Viruses are the most frequent cause. The CDC lists COVID-19, influenza, RSV, human metapneumovirus, parainfluenza virus, and rhinovirus as common viral causes of pneumonia. Less commonly, chickenpox, measles, and adenovirus infections can also reach the lungs. Viral lung infections tend to start with familiar cold or flu symptoms that gradually worsen.
Bacterial lung infections are often more dangerous. A bacterium called Streptococcus pneumoniae is the single largest cause of lung infection deaths globally, responsible for roughly 634,000 deaths in 2023, about 25% of all lower respiratory infection fatalities. Staphylococcus aureus and Klebsiella pneumoniae are the next most common bacterial culprits. Infections picked up in hospitals tend to be harder to treat because the bacteria involved are more likely to be resistant to standard antibiotics.
Fungal lung infections are less common but can be serious, particularly for people with weakened immune systems. A mold called Aspergillus was linked to nearly 68,000 deaths in 2023, highlighting that lung infections aren’t limited to bacteria and viruses.
What Happens Inside Your Lungs
When a pathogen reaches the lower respiratory tract, your immune system floods the area with white blood cells. This causes swelling (edema) in the airway walls and surrounding tissue. In viral infections like influenza, the cells lining the airways can be destroyed outright, and the resulting inflammation fills small passages with fluid and cellular debris.
In pneumonia, the alveoli become lined with thick membranes made of protein and dead cells. These membranes act as a barrier between the air you breathe in and the blood vessels that need to absorb oxygen. The result is that even though you’re breathing, less oxygen actually reaches your bloodstream. This is why pneumonia can cause rapid, shallow breathing and a feeling of air hunger that bronchitis typically does not.
Symptoms That Signal Something Serious
Most lung infections start with a cough, fatigue, and mild fever. Those symptoms alone don’t necessarily mean you need urgent care. What matters is how your breathing changes. A normal adult takes 12 to 20 breaths per minute at rest. Breathing that becomes noticeably rapid and shallow, especially when you’re sitting still, is a sign the infection may be affecting oxygen exchange.
Other warning signs include chest pain that worsens with each breath or cough, confusion or unusual mental fogginess, a fever above 102°F that doesn’t respond to fever reducers, and skin or lips that look bluish. In children, watch for flared nostrils, grunting sounds with each breath, or the skin pulling inward between the ribs during breathing. These signs suggest the lungs are working harder than they should to get enough air.
Who Is Most at Risk
Lung infections can hit anyone, but certain groups face a much higher chance of severe illness. Age is the biggest factor: children under 2 and adults 65 and older are at the greatest risk. Chronic conditions like COPD, asthma, heart disease, diabetes, and kidney disease weaken the body’s ability to fight off infection or put extra strain on organs that are already affected.
People with weakened immune systems, whether from cancer treatment, organ transplant medications, or conditions like HIV, have a harder time clearing infections and building lasting protection from vaccines. Pregnancy also raises the risk because of natural changes in immune function, heart output, and lung capacity. Smoking damages the airway lining and the tiny hair-like structures (cilia) that sweep mucus and pathogens out of the lungs, making smokers significantly more vulnerable.
Living in congregate settings like nursing homes or dormitories increases exposure, and people with neurological conditions that make swallowing difficult, including dementia, Parkinson’s disease, and stroke, are more prone to aspiration pneumonia, where food or saliva enters the lungs.
How Lung Infections Are Diagnosed
For common respiratory viruses, rapid antigen tests can return results in 15 to 30 minutes. These are the familiar at-home tests many people used during COVID-19 and are now available as multiplex versions that can detect both flu and COVID from a single swab. Molecular tests (PCR) are more accurate and detect the actual genetic material of the virus, though results take longer.
When a healthcare provider suspects pneumonia, a chest X-ray is the standard tool. It shows whether fluid or inflammation has settled in the lungs and where. In more complex cases, a CT scan gives a more detailed picture. If a bacterial infection is suspected, a sample of mucus (sputum) can be cultured to identify the specific organism and determine which antibiotics will work against it.
Treatment Depends on the Cause
Viral lung infections, which account for the majority of cases, usually resolve on their own with rest, fluids, and fever management. You typically don’t need a specific antiviral medication, though some are available for influenza and COVID-19 in high-risk patients. Recovery from viral bronchitis takes one to three weeks. Viral pneumonia takes longer, often several weeks before you feel fully back to normal.
Bacterial pneumonia requires antibiotics. Most people with community-acquired bacterial pneumonia improve within a few days of starting treatment, though full recovery can take a month or more, especially in older adults. Hospital-acquired pneumonia is a different challenge. It’s frequently caused by antibiotic-resistant bacteria like MRSA, which limits treatment options and often requires stronger, intravenous medications and a longer hospital stay.
Severe pneumonia of any type may require supplemental oxygen to keep blood oxygen levels adequate while the lungs heal. The sickest patients may need mechanical ventilation in an intensive care unit.
Vaccines and Prevention
Pneumococcal vaccines target Streptococcus pneumoniae, the bacterium responsible for more lung infection deaths than any other single pathogen. The CDC recommends a four-dose vaccine series for all children under 5, given at 2, 4, 6, and 12 to 15 months of age. For adults 50 and older who haven’t been vaccinated, a single dose of the newer vaccines (PCV20 or PCV21) completes the series with no follow-up dose needed.
Annual flu vaccination reduces the risk of influenza-related pneumonia. COVID-19 and RSV vaccines add another layer of protection, particularly for older adults and young infants. Beyond vaccines, the basics matter: frequent handwashing, avoiding close contact with sick individuals, not smoking, and managing chronic conditions all reduce your chances of developing a lung infection or having one turn severe.