A fungal infection in the lungs ranges from mild and self-limiting to life-threatening, depending almost entirely on two factors: which fungus is involved and how well your immune system is functioning. For people with healthy immune systems, most fungal lung infections cause minor flu-like symptoms and resolve without treatment. For people with weakened immunity, the picture is starkly different. Invasive pulmonary aspergillosis, the most common severe form, carries a crude mortality rate of roughly 85% in high-risk groups like those with blood cancers or those in intensive care.
Why Immune Status Changes Everything
Fungal spores are everywhere. You breathe them in daily, and a functioning immune system clears them before they can establish an infection. The infections that become dangerous almost always develop in people whose defenses are compromised. This includes people undergoing chemotherapy, organ transplant recipients on immunosuppressive drugs, those with advanced HIV/AIDS, people taking long-term steroids, and those with chronic lung diseases like COPD or a history of tuberculosis.
Specific conditions that raise risk include acute leukemia, stem cell transplants, solid organ transplants, liver disease, kidney failure, and diabetes. Even a severe case of influenza can open the door to a secondary fungal lung infection, particularly in older adults. Prolonged use of broad-spectrum antibiotics also creates favorable conditions for fungi by wiping out competing bacteria.
Types of Fungal Lung Infections
Not all fungal lung infections behave the same way. The major categories differ in who they affect, how they progress, and how dangerous they become.
Aspergillosis
Aspergillus is the most significant fungal threat to the lungs. It causes a spectrum of disease. In its mildest form, it triggers allergic reactions in people with asthma. In its chronic form, it slowly damages lung tissue over months or years, creating cavities where fungal balls can grow. Chronic pulmonary aspergillosis kills about 18.5% of the roughly 1.8 million people affected globally each year. The invasive form, which spreads rapidly through lung tissue and can enter the bloodstream, is far worse. Over 2 million people develop invasive aspergillosis annually, and approximately 1.8 million die from it. The World Health Organization classifies Aspergillus fumigatus in its critical-priority group of fungal pathogens.
Cryptococcosis
Cryptococcus enters through the lungs but is particularly dangerous because it has a tendency to spread to the brain, causing meningitis. Pulmonary cryptococcosis alone can cause pneumonia-like illness, but the real threat is dissemination. Cryptococcal meningitis affects around 194,000 people per year and kills roughly 147,000 of them, a fatality rate near 76%. This infection predominantly strikes people with advanced HIV. Cryptococcus neoformans also sits in the WHO’s critical-priority group.
Pneumocystis Pneumonia
Pneumocystis jirovecii causes a specific type of pneumonia that became widely recognized during the AIDS epidemic. It remains the most common AIDS-defining illness and also affects people on high-dose steroids or other immunosuppressive therapies. In untreated cases with advanced immune suppression, it can cause severe respiratory failure.
Endemic Fungi
Certain fungi are concentrated in specific geographic regions. Histoplasmosis (common in the Ohio and Mississippi River valleys), coccidioidomycosis or Valley fever (the American Southwest), and blastomycosis (the Great Lakes region) can all infect the lungs of otherwise healthy people. In most healthy individuals, these cause a mild illness that resolves on its own. In immunocompromised people, they can become invasive and fatal. Histoplasma species are classified as high-priority pathogens by the WHO.
What the Symptoms Feel Like
Fungal lung infections often mimic bacterial pneumonia or tuberculosis, which is one reason they’re frequently misdiagnosed. Common symptoms include a persistent cough that doesn’t respond to standard antibiotics, shortness of breath, chest pain, fever, fatigue, and sometimes coughing up blood. Chronic forms develop slowly, with weight loss and worsening breathing over weeks to months. Invasive infections in hospitalized patients can escalate quickly, with high fevers and rapidly worsening respiratory distress.
One of the dangers is how easily these infections get mistaken for something else. Chronic pulmonary aspergillosis, for example, frequently develops in people who’ve recently been treated for tuberculosis, and its symptoms overlap so closely that it’s often incorrectly diagnosed as a TB relapse. An estimated 373,000 new cases develop within 12 months of completing TB treatment each year.
How Fungal Lung Infections Are Detected
Diagnosis typically involves a combination of imaging and blood or fluid tests. On a CT scan, doctors look for characteristic patterns. A “halo sign,” where a dense nodule is surrounded by a hazy ring, is one of the earliest indicators of invasive fungal infection in immunosuppressed patients. Later in the course of disease, an “air-crescent sign” may appear, indicating that a solid area of infection has started to hollow out, usually a sign the immune system is beginning to recover.
Blood tests can detect components shed by growing fungi. One widely used test measures a sugar molecule released by Aspergillus, which has a sensitivity of about 82% in patients with very low white blood cell counts. When the same test is performed on fluid collected directly from the lungs through a bronchoscope, accuracy improves to around 88% sensitivity and 87% specificity. No single test is definitive on its own, so doctors typically combine imaging, blood markers, and sometimes tissue samples to confirm the diagnosis.
Treatment Duration and What to Expect
Three main classes of antifungal drugs are used to treat serious lung infections: azoles (taken as pills), polyenes (given intravenously), and echinocandins (also intravenous). The choice and duration depend on the type and severity of infection.
For invasive aspergillosis, treatment often starts with intravenous medication for at least the first week before switching to oral pills. Chronic pulmonary aspergillosis requires much longer courses, typically six months or more of daily oral antifungal therapy. For mucormycosis, a rarer but aggressive mold infection, treatment frequently lasts months. In one clinical trial, the median treatment duration was 84 days, though some patients needed antifungals for over two years. These are not quick courses of medication. Long treatment timelines bring side effects, including liver strain, and require regular monitoring.
In chronic cases where fungi have formed a ball inside a lung cavity, surgery to remove the affected portion of lung may be necessary alongside drug therapy. Recovery from invasive disease in hospitalized patients can take weeks to months, and some patients face permanent reductions in lung function.
Long-Term Lung Damage
Severe or chronic fungal infections can leave lasting marks on the lungs. Chronic pulmonary aspergillosis progressively destroys lung tissue, creating thick-walled cavities that can be seen on imaging. Fungal growth lines the inside of these cavities, sometimes forming dense sponge-like masses. Over time, these cavities may enlarge, and surrounding lung tissue becomes scarred and fibrotic. Even after successful treatment, the structural damage often persists, leaving patients with reduced lung capacity, chronic cough, and ongoing shortness of breath.
People who develop fungal lung infections after tuberculosis face a compounding problem: TB already damages lung architecture, and a subsequent fungal infection accelerates the destruction. The global burden of this overlap is substantial but likely underestimated because the two conditions are so frequently confused with each other.
Environmental Exposure Risks
Certain environments carry higher concentrations of fungal spores. Water-damaged buildings with visible mold growth are a well-documented risk. Penicillium, Aspergillus, and Stachybotrys (black mold) are among the most commonly found species in contaminated indoor air. Workers in construction, demolition, agriculture, composting, and landscaping face elevated exposure, as do people who work in or renovate older buildings with moisture problems. For healthy individuals, occasional exposure rarely causes serious illness. For people with compromised immunity or pre-existing lung disease, even moderate exposure to concentrated spores can trigger infection.
Geographic exposure matters too. If you live in or travel to regions where endemic fungi are common, activities that disturb soil, like digging, farming, or exploring caves, increase the chance of inhaling infectious spores.