What are the 4 stages of pneumonia?

A black germ on a blue background

An estimated one million older adults in the United States are diagnosed and hospitalized due to pneumonia each year. Even when we take precautions to protect and strengthen our immune systems, we can become more susceptible to pneumonia as we age. Whether you are an older adult yourself or are the caretaker of one, pneumonia can be a scary experience. 

That’s why being aware of the tell-tale signs of pneumonia, often referred to as the four stages of pneumonia, can help save a life. The sooner you recognize the stages in yourself or in a loved one, the sooner you can seek medical treatment and begin recovery. This article will walk you through each stage and how to recognize it.

What is Pneumonia? 

The lungs have air sacs known as alveoli that are located at the end of the bronchial tubes. The alveoli are responsible for ventilation, diffusion, and perfusion (pumping blood through your lungs), so they are responsible for much of our respiration!

Pneumonia is an infection that grows in the alveoli of one or both of the lungs. This infection is generally caused by germs, bacteria, or viruses, and can be contagious.

Viral Pneumonia

Viral Pneumonia is responsible for one-third of reported pneumonia cases. Viral pneumonia is any pneumonia caused by the same viruses that cause the flu and colds. To plant the infection in your alveoli, the virus will enter your lungs and the air sacs and cause your lungs to swell. In turn, this swelling can block your oxygen supply and severely impair your breathing.

Because of the nature of viral pneumonia, it can affect perfectly healthy people who have great immune support. In addition, antibiotics are an ineffective treatment for this form of infection, which makes viral pneumonia much more difficult to treat, more severe in nature, and sometimes fatal.

Bacterial Pneumonia

Bacterial Pneumonia is a form of lung infection caused by bacterial agents (or germs) that invade your lungs. A similar process to viral pneumonia occurs, and the air sacs swell and thus block oxygen flow through the lungs. This form of pneumonia is more likely to affect someone with a weakened immune system or respiratory condition. Antibiotics are used to treat bacterial pneumonia, but the treatment tends to be aggressive and lengthy.

Fungal Pneumonia

Fungal pneumonia is a type of pneumonia with a surprising source—the ground. Fungal pneumonia is caused by breathing in spores or fungal bodies that breed fungal infections in our lungs. Fungal pneumonia can also be caused by a previous infection returning. This form of pneumonia is especially dangerous to those with weakened or compromised immune systems.

The Four Stages 

If pneumonia is left unrecognized and unaddressed, it can prove to be fatal. That’s why it is so important to understand the four stages of pneumonia, the early signs, and symptoms, and learn what to do next.


The first stage of pneumonia is known as congestion -- or consolidation. Your body experiences three different things during this stage: vascular engorgement, intra-alveolar fluid, and multiple bacteria.

  • Vascular engorgement. This is the swelling or engorgement of the veins that run through the lungs. It is caused by increased blood and fluid volume and can be recognized by difficulty breathing.

  • Intra-alveolar fluid. This is the fluid within the alveoli.

  • Multiple bacteria present in the lungs.

The lungs appear dark red and become very heavy due to the increased fluid and blood in the alveoli. The congestion stage of pneumonia is characterized by severe coughing and deep breathing.

Red Hepatization 

Hepatization is the transforming of lung tissue to resemble liver tissue, so red hepatization is the stage where the lungs turn red and resemble the liver. This usually occurs two to three days after the congestion phase. In addition to being red, the lungs will also be airless, firm, and swollen. Vascular congestion and alveolar engorgement persist throughout this stage as well.

During the red hepatization stage, the alveoli are generally full of blood cells. The two main types of blood cells present during this stage are erythrocytes and neutrophils. Erythrocytes are the components of red blood cells that transport carbon dioxide and oxygen to tissues and your lungs. Neutrophils are white blood cells that are responsible for fighting against bacteria, chemicals, and toxic substances.

In addition, epithelial cells and fibrin may be present in the lungs during the red hepatization phase. Epithelial cells are what make up our skin, and they act as shields to protect our bodies from foreign invaders. Fibrin or fibrinogen is an important protein in many of our body’s physiological processes, including repairing damaged tissues and forming blood clots.

Grey Hepatization 

The grey hepatization phase is the third stage of pneumonia and typically occurs two or three days after the red hepatization stage. Similar to the second phase, this phase involves the lungs turning gray, yellow, or brown.

This occurs because grey hepatization is an avascular stage, meaning no blood is involved. Where the red hepatization stage involves the swelling and reddening of the lungs due to increased blood and fluid, the grey hepatization phase involves the opposite. The lungs will lose red blood cells, look more pale, thin, and translucent than usual. Fibrin sticks around during this phase however and continues to form blood clots and repair damaged tissues.


The last stage of pneumonia is called resolution and refers to the recovery of a pneumonia patient. This recovery happens when fibrin is completely digested by the enzymes in the lungs. The waste from leftover fibrin is reabsorbed, excreted, reorganized, or ingested by various waste systems in the body.

Other Symptoms of Pneumonia 

Recognizing the four stages can be critical in saving someone else’s life or your own, but there are some early detection signs to be aware of too. These include:

  • Coughing
  • Mucus that is bloody, yellow, or green
  • Difficulty breathing or shortness of breath
  • Nausea
  • Chest pain
  • Decrease in energy level
  • Fever
  • Chills
  • Loss of appetite
  • Blue nail beds


Being able to recognize the four stages of pneumonia can be lifesaving. Viral, bacterial, and fungal pneumonia can result in respiratory failure, septic shock, infection in your lungs that leads to fluid accumulation, and these can be fatal if not treated immediately.

Infants and older adults are at a greater risk of complications from pneumonia, but some cases of pneumonia in infants and adults don’t display the regular symptoms. To be aware of some of the less common signs of pneumonia that may present in older adults, look for any signs of sudden confusion or low temperature. For infants, watch for vomiting, coughing, and abnormal restlessness.


Once your doctor diagnoses pneumonia, you will likely begin treatment. Sometimes, pneumonia can be taken care of at home. Other times, people need to be hospitalized until they recover. It depends on a variety of factors, including underlying health conditions, immune strength, and how advanced your pneumonia is.

Antibiotics can be used to treat types of bacterial pneumonia. Depending on how severe your pneumonia is and how far it has progressed, these antibiotics may be administered intravenously or orally. However, viral pneumonia cannot be treated with antibiotics.

To treat viral pneumonia, doctors focus more on managing symptoms. This includes maintaining hydration by administering fluids, ensuring that you get enough oxygen, letting your body rest, and the use of some over-the-counter medicines such as ibuprofen or acetaminophen.


There are a variety of ways to prevent pneumonia. The flu vaccine and the pneumococcal vaccine can both help prevent the development of a pneumonia infection, as it is sometimes a result of the flu. Practicing good personal hygiene and safety in public is also a great way to prevent pneumonia and other viruses! Wash your hands with warm water for at least twenty seconds and be aware of your surroundings.

Other things such as regular exercise, eating a balanced diet, and taking care of your immune system health can also make your body less susceptible to contracting pneumonia.

What to Do if You Recognize the Four Stages

If you do recognize one of the four stages or any of the early signs and symptoms, you should see a doctor right away. If you have nails or lips that have turned blue, abnormal body temperature, and mental confusion, call your doctor right away. If you are unsure about your symptoms but are unable to leave your house, consider calling a health professional or making a telemedicine appointment


According to the Centers for Disease Control and Prevention, pneumonia is responsible for over 50,000 fatalities in the US each year. Being aware of the four stages of pneumonia and being able to detect symptoms early is vital and can be lifesaving! If you notice any of the signs, contact a health professional immediately and seek medical care.

Be sure to keep you and your loved one’s health a priority by eating a healthy, balanced diet, exercising regularly, and taking a daily multivitamin.  



Older Adults Hospitalized for Pneumonia in the United States: Incidence, Epidemiology, and Outcomes (agsjournals.onlinlibrary.wiley.com

An unusual cause of fungal pneumonia (ncbi.nim.nih.gov)  

Pneumonia - (health.harvard.edu) 

Effect of pulmonary vascular engorgement on respiratory mechanics in the dog (pubmed.ncbi.nim.nih.gov)

Pneumonia (cdc.gov) 

Fungal pneumonia: a silent epidemic Coccidioidomycosis (valley fever) (cdc.gov)

Four Stages of Pneumonia (bassadvancedurgentcare.com)

Fibrin(ogen) in human disease: both friend and foe (haematologica.org)

Epithelial Cells  (askabiologist.asu.edu)

Erythrocytes – Anatomy & Physiology (pressbooks-dev.oer.hawaii.edu)

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