Medically reviewed by Carina Fung, PharmD, BCPPS

What is pneumonia?

Pneumonia1 is an infection that causes the alveoli—the air sacs inside your lungs—to become inflamed. This inflammation can cause fluids to build up in the alveoli, causing a cough with phlegm or pus, fever, chills, and difficulty breathing. Pneumonia can affect just one lung or both lungs.

Most people who get pneumonia fully recover from the condition. Pneumonia does not usually cause permanent scarring or damage to the lungs. However, a serious infection may cause lung damage. If you have pneumonia, talk with your healthcare provider about what to expect during your recovery.

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The pneumonia virus

Bacterial infections are the most common cause of pneumonia2, although pneumonia can also be caused by viruses. About one-third of cases of pneumonia are viral, and viruses are the most common cause of pneumonia in children younger than age 5.

Though rare, fungi and the inhalation of certain chemicals can also cause pneumonia.

The severity of pneumonia can vary from mild and manageable to severe and even life-threatening. Pneumonia is generally the most serious for people with weaker immune systems: infants and young children, people older than age 65, and those who are immunocompromised.

Because pneumonia is an infection that affects the alveoli, it is different from bronchitis. As its name would suggest, bronchitis infects the bronchi, the main tubes that lead from the windpipe to the lungs.

Pneumonia symptoms

The symptoms of pneumonia can vary from mild to severe3, depending on age, overall health, and the cause of the infection. The mildest symptoms are similar to those of the common cold or a flu; however, the signs and symptoms of pneumonia can last much longer than those of more commonplace illnesses.

Some common signs and symptoms of pneumonia include:

  • A cough that which may produce phlegm (mucus)
  • Pain in the chest when breathing or coughing
  • Fever
  • Sweating, shivering or shaking, and chills
  • Fatigue (exhaustion)
  • Nausea, vomiting, or diarrhea
  • A loss of appetite
  • Shortness of breath or difficulty breathing
  • Lower than normal body temperature (particularly in adults over 65 and people with weak immune systems)
  • Confusion or changes in mental awareness (also most common in adults aged 65 and older)

The symptoms of pneumonia may come on quickly and may gradually worsen over time. In some cases, when a person already has a cold, the development of a fever and/or worsening symptoms can signal the onset of pneumonia.

Some signs and symptoms may indicate serious health complications. It’s best to call your provider if4:

  • Your cough is severe and is not getting better

  • Your fever is not going away or is getting worse

  • You experience shortness of breath or difficulty breathing

  • You do not feel better or still have a fever 3 days after starting antibiotics

Seek immediate medical help if you experience difficulty breathing, severe chest pain, develop a bluish color in your fingertips or lips (cyanosis, which indicates a low concentration of oxygen in the blood), or cough up blood.

Most people with pneumonia begin to feel better within 3–5 days of their first signs and symptoms. However, making a full recovery from pneumonia can take as long as a few months. Some studies have shown that pneumonia patients still show moderate to severe symptoms 30 days after diagnosis5.

The time it takes to recover from pneumonia varies depending on the individual. Recovery time may take longer if you have other pre-existing medical problems, such as COPD or asthma. If you find that your recovery is very slow or your symptoms are worsening, contact your healthcare provider.

Pneumonia types

There are several types of pneumonia, each classified by the cause of the infection. The different types of pneumonia are:

  • Bacterial pneumonia: Bacterial pneumonia is caused by infection with a bacterial pathogen (intruding substance). This type of pneumonia often occurs when the body or immune system have already been weakened in some way, possibly through illness, old age, or an immune disorder. The bacteria that most commonly causes pneumonia is Streptococcus pneumoniae. One form of bacterial pneumonia, Legionnaires’ disease, is caused by the legionella bacteria (L. pneumophila). This bacteria is found naturally in freshwater. Bacterial pneumonia can infect people of all ages. However, your risk for developing this infection increases if you have a respiratory illness or viral infection, are immunocompromised, consume an excess of alcohol, smoke cigarettes, or are physically debilitated.
  • Viral pneumonia: Viral infections cause roughly one-third of all cases of pneumonia. One common viral infection that leads to pneumonia is influenza (the flu). Having viral pneumonia may put you at an increased risk for developing bacterial pneumonia as well.
  • Mycoplasma pneumonia: This form of pneumonia is caused by the bacteria mycoplasma pneumoniae. Mycoplasma pneumonia can affect all age groups and generally causes a milder, more widespread form of the illness.
  • Aspiration pneumonia: This type of pneumonia occurs when substances such as food, liquid, vomit, or saliva are inhaled into the lungs. People who have had a stroke or other neurological conditions are at the highest risk for developing aspiration pneumonia.
  • Other pneumonias: Other less common pneumonias can result from other types of infections, including those caused by fungi.

What is walking pneumonia?

You may have heard the term “walking pneumonia” and not known what it meant. Walking pneumonia6 is a non-medical term that refers to a mild case of pneumonia. It is used to describe patients with pneumonia that are not completely inhibited by the illness (and, as such, can do activities like walking around, instead of lying in bed or in a hospital).

Walking pneumonia is caused by the relatively mild Mycoplasma pneumoniae bacteria. Because this viral infection is not particularly dangerous, patients with this illness can usually keep going about their daily activities.

Walking pneumonia still includes some unpleasant symptoms, including cough, fever, chest pains, chills, and headache. It can feel like a bad cold that persists for a long time.

Pneumonia causes

The most common cause of pneumonia is an infection by bacteria and viruses transferred through the air you breathe. In rare instances, pneumonia can be caused by a fungus, yeast, or parasite.

The different types of pneumonia can also be classified according to where a patient acquired the infection. These include community-acquired pneumonia7, hospital-acquired pneumonia, healthcare-acquired pneumonia, and aspiration pneumonia.

  • Getting community-acquired pneumonia8 is the most common way of acquiring pneumonia. This mode of infection occurs in daily life, outside of hospitals or other healthcare facilities. Some people catch pneumonia while in the hospital being treated for another illness. Hospital-acquired pneumonia9 can be very serious, as the bacteria that cause it may be more resistant to antibiotics than typical bacteria. Furthermore, patients who get hospital-acquired pneumonia are already sick, and their weakened immune systems may have a harder time fighting off pneumonia than those of healthy individuals. People who are on ventilators (assisted breathing machines), which are often used in intensive care units (ICUs), are at higher risk for developing this type of pneumonia.

Healthcare-acquired pneumonia is also a bacterial infection. This type of pneumonia develops in individuals who live in long-term care facilities (such as a senior living center) or who receive outpatient medical care, such as chemotherapy or kidney dialysis centers. Like hospital-acquired pneumonia, health care-acquired pneumonia can also result from infection with antibiotic-resistant.

Who gets pneumonia?

Pneumonia can affect anyone. However, children aged 2 or younger and adults aged 65 or older are at the highest risk for developing pneumonia.

Other factors and conditions may increase your likelihood for developing pneumonia. Some risk factors10 include:

  • Being hospitalized: Being hospitalized in an intensive care unit puts you at higher risk for developing the illness—especially if you're on a machine that helps you breathe (a ventilator).
  • Chronic disease: You're more likely to get pneumonia if you have asthma, chronic obstructive pulmonary disease (COPD), or heart disease.
  • Smoking: Smoking damages your body's natural defenses against the bacteria and viruses that cause pneumonia.
  • Weakened or suppressed immune system: People with immune conditions (such as HIV/AIDS) those, who have had organ transplants, and those who receive chemotherapy or long-term steroids are at increased risk for pneumonia.
  • Having pre-existing lung problems

Disclaimer: The information on this site is generalized and is not medical advice. It is intended to supplement, not substitute for, the expertise and judgment of your healthcare professional. Always seek the advice of your healthcare professional with any questions you may have regarding a medical condition. Never disregard seeking advice or delay in seeking treatment because of something you have read on our site. RxSaver makes no warranty as to the accuracy, reliability or completeness of this information.

If you are in crisis or you think you may have a medical emergency, call your doctor or 911 immediately.