Pneumonia Symptoms and Causes
Updated on March 16, 2026
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There are many different causes of pneumonia, including bacteria, viruses, and fungi. When these germs enter the lungs, they can overpower the immune system and invade delicate lung tissues. Once a pathogen infects the lungs, the air sacs become inflamed and fill with fluid and pus, leading to the symptoms of pneumonia.
Some types, such as those that develop due to bacterial or viral infections, are contagious. Others, like fungal pneumonia, can’t spread from person to person. Contagious forms of pneumonia can transmit between people through coughing, sneezing, touching, and even breathing.
Symptoms
Pneumonia symptoms can range from mild to severe. They may differ depending on the type of pneumonia and the age of the person with the infection. However, common symptoms may include:
- Chest pain while breathing
- Chills
- Coughing that may or may not produce mucus
- Fever
- Low blood oxygen when measured with a pulse oximeter
- Breathlessness
You might also experience the following:
- Headaches
- Muscle pain
- Fatigue
- Nausea and vomiting
- Diarrhea
Older adults might experience a low instead of a high temperature, weakness, and confusion. Infants can also experience atypical symptoms, such as:
- A blue tint to the lips and skin
- Making grunting sounds
- Pulling the ribs inward while breathing
- Breathing rapidly
- Widening the nostrils every time they breathe
Types
Different causes of pneumonia can also lead to varying symptoms.
Bacterial Pneumonia
Bacteria are a common cause of pneumonia in adults. They can cause a series of classic symptoms, including:
- A cough that produces discolored or bloody mucus
- Fever
- Shortness of breath
Other bacterial pneumonia symptoms include:
- High fever
- Chills
- Rapid breathing
- Pain when coughing or breathing deeply
- Shortness of breath
- Exhaustion
- Loss of appetite
Bacterial pneumonias tend to be very severe and cause more noticeable symptoms than other types of pneumonia, with a higher likelihood of needing hospital treatment.
Bacterial pneumonia may follow a viral infection, such as a cold or the flu (influenza). This type of pneumonia may affect just one area of a lung and is referred to as lobar pneumonia.
Types of bacteria that cause pneumonia include:
- Streptococcus pneumoniae, the most common cause in the United States
- Legionella pneumophila, the cause of Legionnaires’ disease, or legionellosis
- Mycoplasma pneumoniae, which usually infects younger adults who work in crowded areas, such as schools, homeless shelters, or prisons
- Chlamydophila pneumoniae, which causes a mild pneumonia infection that usually affects people older than 60 years
- Haemophilus influenzae type B (Hib)
Hospital-Acquired Pneumonia
This form of pneumonia is acquired during or after a hospital stay, and it can be severe and even fatal. It’s often more difficult for people to fight off this infection because they’re already sick, and the germs and bacteria in the hospital environment may be more resistant to treatment than those out in the community.
The first sign of hospital-acquired pneumonia may be confusion or cognitive changes in older adults. Other symptoms include:
- Fever or chills
- A cough with greenish phlegm
- Loss of appetite
- Nausea and vomiting
- Chest pain
- Shortness of breath
- Decreased blood pressure.
- A drop in oxygen levels in the blood
You may have a higher risk of hospital-acquired pneumonia if the following apply to you:
- You’re an older adult.
- You’ve had chest surgery or other major surgery.
- You have chronic lung disease.
- You are immunocompromised.
- You have alcohol use disorder.
- You experience swallowing problems and breathe saliva or food into your lungs, which can happen after a stroke.
- You’re on a ventilator.
- You’re experiencing cognitive side effects and reduced mental alertness due to medication or illness.
Walking Pneumonia
A mild case of bacterial or viral pneumonia, often called walking pneumonia, features symptoms similar to the common cold, including:
- Persistent dry cough that often gets worse at night
- Low-grade fever
- Shortness of breath
- Fatigue or tiredness
- Chest pain that gets worse when you take a deep breath or cough
- Loss of appetite
- Sore throat
Viral Pneumonia
Viruses account for approximately one-third of all pneumonias. Viral pneumonias tend to clear up in about one to three weeks, but they can increase your risk of bacterial pneumonia. They’re usually less severe than bacterial pneumonias, but some viruses like influenza and SARS-CoV-2 can be very severe.
At first, the symptoms of viral pneumonia may be similar to the symptoms often associated with the flu, except you may experience a dry cough that does not produce phlegm. You may also develop a fever, muscle pain, weakness, and a headache.
However, within a couple of days, these symptoms typically worsen.
Adults with viral pneumonia can also expect to develop:
- Worsening cough
- Increasing breathlessness
- More severe muscle pain
- Sometimes, high fever and a blue tint to the lips
The influenza virus is a common cause of viral pneumonia, which tends to be more severe in individuals with heart or lung disease, adults ages 65 and older, and young children. Individuals with compromised immune systems also have a higher risk of influenza progressing to pneumonia.
Not only can influenza cause pneumonia — it can also predispose people to bacterial pneumonia. This is a good reason to get the yearly flu shot.
Respiratory syncytial virus (RSV) pneumonia, another type of viral pneumonia, is usually a mild infection that clears up in about a week or two. It can be more severe and is more common in young children and older adults. In fact, RSV is the most common cause of pneumonia in children younger than 12 months, according to the Centers for Disease Control and Prevention.
SARS-CoV-2, the virus that causes COVID-19, can also cause viral pneumonia. COVID pneumonia often affects both lungs and tends to spread slowly, lasting longer and causing more damage than other types of pneumonia. If you develop COVID pneumonia, you’ll likely need admission to the hospital.
Fungal Pneumonia
The symptoms of fungal pneumonia are often similar to those of other forms of pneumonia, including fever, dry cough, shortness of breath, and fatigue. However, the symptoms and their severity may depend on the type of fungus. Four types of fungi that live in soil are known causes of pneumonia:
- Coccidioides immitis and Coccidioides posadasii are two related fungi common to the southwestern United States. Both can cause coccidioidomycosis, also known as cocci or valley fever.
- Histoplasma capsulatum is found in the central and eastern United States, especially areas around the Ohio and Mississippi River valleys, and it causes a disease called histoplasmosis.
- Cryptococcus is a fungi present in soil and bird droppings all across the country.
- Blastomyces, which can cause blastomycosis, is found largely in the midwestern, south-central, and southeastern United States.
Most people who inhale these fungi don’t get sick, but if your immune system doesn’t function well, you may develop pneumonia.
Another fungus, Pneumocystis jirovecii, can generate an infection in premature, malnourished infants and in people with weakened immune systems, such as those who have HIV or AIDS. However, because this type of pneumonia typically affects individuals with weakened immune systems, the symptoms tend to develop more rapidly and patients often experience a high fever.
In hospitalized patients with compromised immune systems, opportunistic fungal pneumonia can occur and may involve multiple fungi, including candida and aspergillus.
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Complications
Without treatment, pneumonia can become severe. People with severe pneumonia experience higher fevers, along with gastrointestinal symptoms, such as vomiting and diarrhea, as well as:
- Difficulty breathing
- Excessive sweating
- Rapid breathing and heart rate
- Bluish tint to lips and nails from a lack of oxygen in the blood
Additional potential complications include bacteremia, in which bacteria from the lungs can enter the bloodstream and spread the infection to other parts of the body. A bacterial infection of the lungs can also lead to a pus-filled cavity in the lung called an abscess. Both of these complications are treatable with antibiotics. Other serious complications can include infection of the space outside the lung (empyema) or pathogens spreading to the brain and causing meningitis.
If you have flu-like symptoms that persist or worsen despite treatment, consult a healthcare professional. Those who have trouble breathing should go to the emergency department immediately.
The Takeaway
- Pneumonia has multiple potential causes, including bacteria, viruses, and fungi, each of which can lead to a lung infection.
- Symptoms of pneumonia range from mild to severe and may include chest pain, cough, fever, and shortness of breath, possibly varying by type and age.
- While bacterial pneumonia typically causes more severe symptoms, viral and fungal pneumonias can also pose serious health risks, highlighted by complications such as pneumonia from COVID-19 requiring hospital care.
- Seek immediate medical attention if flu-like symptoms worsen or respiratory symptoms are severe, as untreated pneumonia can lead to critical complications like bacteremia or lung abscesses.
Additional reporting by George Vernadakis.
Resources We Trust
- Cleveland Clinic: Pneumonia
- American Lung Association: Pneumonia Treatment and Recovery
- Centers for Disease Control and Prevention: Pneumococcal Vaccination
- Franciscan Health: Is It Bronchitis or Pneumonia?
- Children’s Hospital Colorado: Pneumonia in Children
EDITORIAL SOURCES
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Resources
- Pneumonia. Johns Hopkins Medicine.
- Pneumonia. Cleveland Clinic. November 15, 2022.
- Learn About Pneumonia. American Lung Association. October 15, 2025.
- Pneumonia Symptoms. National Heart, Lung, and Blood Institute. March 24, 2022.
- Pneumonia Causes and Risk Factors. National Heart, Lung, and Blood Institute. March 24, 2022.
- Pneumonia. Mayo Clinic. June 13, 2020.
- About Mycoplasma pneumoniae Infection. Centers for Disease Control and Prevention. October 17, 2024.
- Chlamydia pneumoniae Infection. Centers for Disease Control and Prevention.
- Hospital-Acquired Pneumonia. MedlinePlus. August 13, 2023.
- What’s the Difference Between Walking Pneumonia and Pneumonia? Cleveland Clinic. November 25, 2024.
- What Are the Symptoms of Pneumonia? American Lung Association. August 14, 2025.
- The Connection Between Influenza and Pneumonia. American Lung Association. June 3, 2025.
- About RSV. Centers for Disease Control and Prevention. July 8, 2025.
- COVID Pneumonia. Cleveland Clinic. August 10, 2022.
- Valley Fever. Mayo Clinic. September 20, 2025.
- About Histoplasmosis. Centers for Disease Control and Prevention. April 24, 2024.
- About Blastomycosis. Centers for Disease Control and Prevention. April 24, 2024.
- Pneumocystis Pneumonia Basics. Centers for Disease Control and Prevention. April 24, 2024.
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Michael S. Niederman, MD
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Michael S. Niederman, MD, is the lead academic and patient quality officer in the division of pulmonary and critical care medicine at Weill Cornell Medical Center in New York City;...
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Mary Elizabeth Dallas is a journalist with more than 15 years of experience who specializes in health news and feature stories. She covers public health issues, including microbial...