Pneumonia Symptoms, Causes, Treatment & Warning Signs
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Introduction
Pneumonia is a lung infection that can range from mild to life-threatening1,8. It causes swelling in one or both lungs1,8. Tiny air sacs may fill with fluid or pus1,3.
This fluid can make breathing painful3. It can also reduce how much oxygen enters the body3,6. Pneumonia symptoms may look like flu, COVID-19, or another lung illness7,8.
Symptoms alone cannot confirm pneumonia or show which germ caused it2,6. A medical exam and tests may be needed6.
Learning about pneumonia symptoms, causes, treatment and warning signs can help you seek timely care. This guide also covers risk factors, tests, prevention, and emergency signs.
Overview: What Pneumonia Is and Who Is at Risk
How pneumonia affects the lungs
The lungs contain tiny air sacs called alveoli3. In healthy lungs, these sacs fill with air during breathing3. Pneumonia causes the sacs and nearby tissue to swell3,4.
The air sacs may fill with fluid or pus1,3. This makes it harder for oxygen to enter the blood3,6. The infection may affect one lung or both lungs1,9.
Lobar pneumonia affects one or more lung sections called lobes9. Bronchopneumonia causes infected patches across the lungs9. Both forms can range from mild to severe1,8.
The cause can affect how serious the illness becomes1. Age and general health also affect the risk of severe disease1,8. Poor immune health may make it harder to fight the infection8,9.
Types of pneumonia
Doctors may group pneumonia by its cause or where it began1,2. Main types include:
Community-acquired pneumonia begins outside a hospital or care center2.
Healthcare-associated pneumonia develops during or after healthcare exposure2.
Aspiration pneumonia starts when unwanted material enters the lungs7.
Bacterial pneumonia is caused by bacteria1.
Viral pneumonia is caused by a virus in the breathing system1.
Fungal pneumonia is caused by fungi and is less common1,2.
Aspiration occurs when material enters the airway and reaches the lungs7. This may cause swelling and infection in the lungs7.
Bacterial pneumonia can begin on its own1. It can also develop after a viral illness, such as flu1. Viral pneumonia is often mild, but some cases need hospital care1.
People at higher risk of severe illness
Anyone can develop pneumonia3. However, some people have a higher risk of serious illness3,8.
Higher-risk groups include:
Infants and young children8
People who smoke cigarettes9,10
People with long-term heart or lung disease3,9
People with weakened immune systems8,9
People in poor general health9
People who drink alcohol heavily9,10
People who recently had surgery or hospital care2,9
Pneumonia can be more dangerous in babies and older adults4,8. Long-term health problems may also raise the risk of severe disease3,9.
People at high risk should contact a clinician about possible signs of pneumonia. Prompt care is important when symptoms worsen or affect breathing.
Symptoms and How They May Differ
Common pneumonia symptoms
Pneumonia symptoms differ between people7,8. Age, health, cause, and severity may shape the symptoms8. Symptoms may begin quickly or develop over several days4,10.
Common signs of pneumonia include:
Yellow, green, or bloody mucus7,8
Fever, sweating, or chills5,8
Chest pain during breathing or coughing5,8
A person may not have every symptom7. Mild pneumonia can feel like a cold or flu8. However, pneumonia symptoms may last longer8.
Chest pain may result from swelling in tissues near the lungs5. The pain may become worse during a deep breath or cough5,8.
Severe pneumonia can lower the amount of oxygen in the blood6. This can cause serious breathing problems3,6. Hospital care may be needed in severe cases1,6.
Mucus may differ in color and amount7,8. A cough may also be dry. A cough pattern alone cannot confirm pneumonia6,7,8.
Symptoms in older adults and children
Older adults do not always have typical pneumonia symptoms8. They may develop new confusion or changes in awareness8. They may also have a lower-than-normal temperature8.
Weakness may occur with other signs of pneumonia4,8. These changes can matter even when fever or cough seems mild8.
Infants and young children have a higher risk of severe pneumonia8. Their symptoms may differ from those seen in adults8. Feeding or breathing problems in an infant need prompt medical advice.
Age and general health can affect how severe pneumonia becomes1,8. The cause of the infection also plays a part1,8. Symptoms alone cannot show the full level of risk1,6,8.
Pneumonia versus a cold, flu, or bronchitis
Pneumonia often causes cough, fever, tiredness, and breathing problems5,8. These symptoms can also occur with other breathing illnesses7,8.
Flu and COVID-19 can cause viral pneumonia7. A viral illness may also occur before bacterial pneumonia1. This later infection is called a secondary bacterial infection.
Symptoms alone cannot separate pneumonia from flu or COVID-196,7,8. They also cannot rule out bronchitis or a cold6,8. A clinician may need to examine the lungs and order tests6.
Mild pneumonia can resemble a cold or flu8. Pneumonia symptoms may last longer or become more severe8. Trouble breathing needs medical attention, whatever the suspected cause.
A medical exam provides more information than symptoms alone6. Testing can also show whether blood oxygen is too low6.
Causes, Spread, and Risk Factors
Bacterial, viral, and fungal causes
Bacteria and viruses are common causes of pneumonia2. Fungi and parasites cause pneumonia less often2. Clinicians cannot always identify the exact germ2,6.
Streptococcus pneumoniae is a common cause of bacterial pneumonia1,9. Other bacterial causes include Mycoplasma pneumoniae and Legionella pneumophila1. Haemophilus influenzae type b can also cause pneumonia1.
Viruses that infect the breathing system may cause viral pneumonia1. Flu and COVID-19 are common viral causes7. Flu can also occur before bacterial pneumonia develops1.
Fungal pneumonia is less common than bacterial or viral pneumonia1,2. Pneumonia caused by a parasite is also less common2. Treatment depends on the likely cause and severity7.
How pneumonia develops or spreads
Pneumonia begins when an infection affects the lungs3,7. The immune response causes swelling and fluid in the air sacs7. These changes can make breathing harder3,7.
Some viruses and bacteria linked to pneumonia can spread between people3,10. Direct contact can spread certain infections3. However, exposure does not mean that a person will develop pneumonia1,8.
Healthcare settings may have different germs than the wider community2. This helps doctors group the illness and plan care2.
Pneumonia can also develop after aspiration7. Aspiration happens when unwanted material enters the breathing tube7. That material can then travel into the lungs7.
Factors that raise pneumonia risk
Several health and lifestyle factors can raise the risk of pneumonia8,9,10. They include:
A weakened immune system8,9
Long-term heart or lung disease3,9
Recent hospital or healthcare exposure2,9
Aspiration into the lungs7
Smoking raises the chance of developing pneumonia9,10. Heavy alcohol use is also linked with greater risk9,10.
People in hospitals may meet different germs than people in the community2. Recent hospital care can affect the type of pneumonia involved2.
Poor health may weaken the body’s ability to fight a lung infection9. A weak immune system can also raise the risk of severe illness8,9.
Risk factors do not prove that a person has pneumonia. Clinicians review them with symptoms, exam findings, and test results6,8.
Diagnosis and Treatment
How clinicians diagnose pneumonia
A clinician will ask about symptoms and medical history6. The next step is often a physical exam6. This includes listening to the lungs with a stethoscope6.
Crackling or bubbling lung sounds can suggest pneumonia6. However, an exam may not provide enough information6. Tests can help support the diagnosis6.
Pulse oximetry: A small sensor checks the oxygen level in the blood6.
Chest X-ray: This image shows the location and extent of pneumonia6.
Blood tests: These look for infection and may suggest a cause6.
Sputum test: A laboratory checks mucus coughed from the lungs6.
A chest X-ray can help diagnose and locate pneumonia6. It generally cannot identify the germ that caused it6.
Blood tests may help confirm an infection6. Sputum tests may help find the cause6. Still, the exact germ is not always identified2,6.
Pulse oximetry shows whether the blood carries enough oxygen6. Pneumonia can block enough oxygen from reaching the blood6.
The choice of tests depends on the symptoms and illness severity. Severe illness or an unclear diagnosis may lead to more testing6.
Treatment based on cause and severity
Pneumonia treatment depends on its likely cause and severity7. Age and general health can also guide treatment choices1,8.
Antibiotics treat bacterial pneumonia4. Antibiotics do not treat viral pneumonia4. A clinician should decide whether antibiotics are needed.
Take prescribed medicine as directed. Contact the prescribing clinician if you have questions about its use.
Some cases of viral pneumonia improve without medicine that targets the virus1. Other cases can become severe and need hospital care1.
Antiviral medicine may help in selected viral infections6,7. Antifungal medicine may treat pneumonia caused by fungi6,7.
Severe pneumonia may require treatment in a hospital1,6. Hospital care may include oxygen or medicine given through a vein6. Medicine given this way is called intravenous treatment.
Low blood oxygen may require oxygen treatment6. The care team can use pulse oximetry to track oxygen levels6.
Pneumonia treatment should match the suspected cause7. It should also fit the person’s health and illness severity1,7,8.
Recovery and supportive care
Rest may support the body while it fights an infection. Follow your clinician’s advice about fluids and fever relief. Ask before using a cough medicine.
Recovery time differs from person to person1,4. A healthy person may recover within a few weeks4. Full strength may take several months to return4.
Age, cause, health, and severity can affect recovery1,8. Follow-up is important when symptoms do not improve as expected.
Contact the treating clinician if cough or fever gets worse. Worsening weakness or chest pain also needs medical advice. New or worse breathing problems need prompt review.
Do not share prescribed medicine with another person. Antibiotics treat bacterial pneumonia but do not treat viral pneumonia4.
Safe pneumonia treatment begins with a sound diagnosis. Symptoms, causes, treatment, and warning signs should be reviewed together.
When to See a Doctor: Warning Signs and Complications
When pneumonia is an emergency
Severe breathing trouble may mean that the body is not getting enough oxygen3,6. Blue or gray lips or skin may signal dangerously low oxygen. New confusion can occur in older adults with pneumonia8.
Blue or gray lips, face, or skin
Severe or fast-worsening chest pain
New confusion or a major change in awareness
Inability to wake or stay awake
Signs of dangerously low oxygen
Pneumonia can stop the lungs from moving enough oxygen into the blood6. Severe breathing trouble may therefore be an emergency3,6. Blue or gray skin and new confusion also need urgent review.
Do not drive if you are confused or very short of breath. Contact local emergency services for immediate help.
Worsening symptoms need urgent medical review. Persistent fever, dehydration, or coughing blood also need medical advice. High-risk people should seek help when pneumonia symptoms appear.
Older adults may have confusion or a low body temperature8. These signs can occur instead of common symptoms8. Families should take a sudden change in awareness seriously.
Knowing when pneumonia is an emergency can help prevent delays. Do not wait when breathing, awareness, or skin color changes quickly.
Possible pneumonia complications
Pneumonia can cause life-threatening problems1,4. The risk is higher in babies and older adults4,8. People in poor health also face greater risk4,8.
Severe pneumonia can lead to:
Respiratory failure means the lungs cannot supply enough oxygen. Sepsis is a dangerous response to an infection. A lung abscess is a pocket of pus in lung tissue.
Fluid can also collect in the space around a lung. This is called a pleural fluid problem. Severe pneumonia can cause any of these complications.
Pneumonia may become life-threatening when severe complications occur1,4. Fast changes in breathing or awareness need emergency care. Blue or gray skin also requires immediate evaluation.
Vaccines and practical prevention
Vaccines can prevent pneumonia caused by certain germs3,4. They cannot prevent every case because many germs can cause pneumonia1,2.
Pneumococcal vaccines reduce risk from specific pneumococcal infections3,4. Flu vaccines can lower the risk linked to influenza infections3,4. COVID-19 and other advised vaccines may reduce risk from specific infections3,4,7.
Ask a healthcare professional which vaccines are right for you. Vaccine needs may vary by age and health risk.
Other practical steps include:
Follow infection-control steps in care settings.
Limit close contact with people who have breathing infections.
Avoid cigarette smoke when possible.
Follow care plans for long-term health problems.
Smoking raises pneumonia risk, so quitting may help lower that risk9,10. Infection-control steps may limit contact with germs that spread between people3,10.
Prevention is part of understanding pneumonia symptoms, causes, treatment and warning signs. Vaccines and healthy habits may lower risk1,3,4. However, they cannot prevent every case1,2.
Conclusion
Pneumonia causes swelling in the air sacs of one or both lungs1,8. The sacs may fill with fluid or pus1,3. This can reduce oxygen intake and make breathing harder3.
Common symptoms include cough, fever, chills, tiredness, and shortness of breath3,5,8. Chest pain may worsen during breathing or coughing5,8. Older adults may develop confusion or a low temperature8.
Bacteria and viruses are common causes of pneumonia2. Fungi and parasites cause it less often2. Streptococcus pneumoniae is a common bacterial cause1,9.
Antibiotics treat bacterial pneumonia but do not treat viral pneumonia4. Chest X-rays can help find and locate pneumonia6. However, they cannot identify the exact germ6.
Recognizing pneumonia symptoms, causes, treatment and warning signs can support timely care. Severe breathing trouble needs urgent medical evaluation. Blue or gray skin and new confusion also need emergency care.
Recommended vaccines can lower risk from some infections3,4. Hand hygiene, infection control, and smoking cessation may provide more protection3,9,10.
Evidence used in this article
- 1. Pneumonia | Bronchopneumonia | MedlinePlus
Pneumonia is an infection in one or both of your lungs. It causes the air sacs of your lungs to fill up with fluid or pus. Pneumonia can range from mild to severe, depending on what caused it, your age, and your overall health.
...
### What causes pneumonia?
...
Bacterial, viral, and fungal infections can cause pneumonia.
...
Bacteria are the most common cause. Bacterial pneumonia can occur on its own. It can also develop after you've had certain viral infections such as a cold or the flu. Sever
- 2. About Pneumonia | Pneumonia | CDC
About Pneumonia | Pneumonia | CDC
# About Pneumonia
Feb. 25, 2026
Español
## Key points
- Bacteria and viruses are common causes of pneumonia (a lung infection).
- Fungi and parasites are less common causes.
- Germs that commonly cause pneumonia in the community are different from those in healthcare settings.
- Clinicians aren't always able to find out which germ caused someone to get sick with pneumonia.
- Talk to a healthcare provider if you have concerns about pneumonia.
## Overview
P
- 3. Pneumonia
Pneumonia Skip to main content
Overview
Pneumonia is a form of acute respiratory infection that is most commonly caused by viruses or bacteria. It can cause mild to life-threatening illness in people of all ages, however it is the single largest infectious cause of death in children worldwide.
Pneumonia killed more than 808 000 children under the age of 5 in 2017, accounting for 15% of all deaths of children under 5 years. People at-risk for pneumonia also include adults over the age of 65 an
- 4. Overview: Pneumonia - InformedHealth.org - NCBI Bookshelf
People who develop pneumonia often feel very ill quite suddenly: They may have a high fever, chills, a cough and get out of breath easily. This happens because small air sacs (alveoli) in their lungs are inflamed, along with the surrounding lung tissue.
...
Pneumonia is often caused by bacteria. It can then usually be successfully treated with antibiotics. There are also vaccinations that can prevent pneumonia that's caused by certain germs.
...
People who are otherwise in good health generally
- 5. Pneumonia- Patient Information | BMJ Best Practice US
Pneumonia- Patient Information | BMJ Best Practice US
Patient information
# Patient information from BMJ
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## Pneumonia
Last published:May 02, 2025
Pneumonia is an infection in the lungs. It can be serious, so it's important to get treatment quickly.
This information explains what pneumonia is, the symptoms to look out for, and how it’s treated.
### What is pneumonia?
Pneumonia is an infection that causes inflammation (swelling) in your lungs. It is caused by either a virus, bacteria
- 6. Pneumonia - Diagnosis and treatment - Mayo Clinic
Your doctor will start by asking about your medical history and doing a physical exam, including listening to your lungs with a stethoscope to check for abnormal bubbling or crackling sounds that suggest pneumonia.
...
If pneumonia is suspected, your doctor may recommend the following tests:
...
- Blood tests. Blood tests are used to confirm an infection and to try to identify the type of organism causing the infection. However, precise identification isn't always possible.
- Chest X-ray. This h
- 7. Pneumonia: Causes, Symptoms, Diagnosis & Treatment
Pneumonia is inflammation and fluid in your lungs caused by a bacterial, viral or fungal infection. It makes it difficult to breathe and can cause a fever and cough with yellow, green or bloody mucus. The flu, COVID-19 and pneumococcal disease are common causes of pneumonia. Treatment depends on the cause and severity.
...
Pneumonia causes your lung tissue to swell. It can cause fluid or pus in your lungs.
...
Pneumonia is an infection that causes inflammation and fluid in the small air sacs of
- 8. Pneumonia - Symptoms and causes - Mayo Clinic
Pneumonia is an infection that inflames the air sacs in one or both lungs. The air sacs may fill with fluid or pus (purulent material), causing cough with phlegm or pus, fever, chills, and difficulty breathing. A variety of organisms, including bacteria, viruses and fungi, can cause pneumonia.
...
Pneumonia can range in seriousness from mild to life-threatening. It is most serious for infants and young children, people older than age 65, and people with health problems or weakened immune systems
- 9. Pneumonia | Johns Hopkins Medicine
Pneumonia | Johns Hopkins Medicine
# Pneumonia
## What is pneumonia?
Pneumonia is an infection of one or both of the lungs caused by bacteria, viruses, or fungi. It is a serious infection in which the air sacs fill with pus and other liquid.
Lobar pneumonia affects one or more sections (lobes) of the lungs.
Bronchial pneumonia (also known as bronchopneumonia) affects patches throughout both lungs.
## What causes pneumonia?
There are more than 30 different causes of pneumonia, and they’re
- 10. Pneumonia: Symptoms, Causes, and Treatment
Pneumonia is a lung infection that can range from mild to so serious that you have to go to the hospital. It happens when an infection causes air sacs in your lungs (the alveoli) and tubes in your airways that connect to them (bronchioles) to fill with fluid or pus. That can make it hard for you to breathe in enough oxygen.
...
Anyone can get this lung infection. But children younger than 2 and adults 50 years old and up are at higher risk. That’s because their immune systems might not be strong
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