What are the 4 Stages of Pneumonia?

Pneumonia is inflammation of lung parenchyma. It can occur due to viruses, bacteria, fungus even cal irritation. It can affect any age group including the newborn and elderly. The patient will present with cough, fever, shortness of breath, and respiratory distress. If severe, it can even cause deranged mental status and confusion due to low oxygen delivery to the brain. If you want to know more about pneumonia go ahead and read this wonderful article. But for now, we will see the 4 stages of pneumonia.



A patient who has pneumonia usually passes through 4 stages. These are : –

  • Congestion/consolidation
  • Red hepatization
  • Gray hepatization
  • Resorption and restoration


This stage of pneumonia commonly appears in the first 24 hours of infection. In this stage, your lung will be engorged and will have intra-alveolar edema. The infectious organism will be accumulated in the lung. Also, the air space will be filled with fluid so it will be difficult for air exchange between blood vessels and alveoli. At this stage of pneumonia, you will experience toxicity symptoms like cough, shortness of breath, and fast breathing. Clinically your respiratory rate will be increase and the oxygen concentration of blood will be decreased.


At this stage, blood cells and immune cells will be pooled to the infection site (lung) which makes your lung congested and appear red. Due to an activated immune system, you will experience fever, chill, and rigor. And due to more fluid in the lung, it will be more and more difficult to breathe. If severe, you might experience blue or blackish lips and extremities. This stage starts after 2 – 3 days of the symptom and stays for 2 – 4 days.


Microscopically there will be cellular exudates of immune cells, engulfed bacteria, red blood cells, and epithelial cells. Even though fibrin starts to replace the edema at this point, the lung appears red due to erythrocytes.


This stage occurs 2 – 3 days after red hepatization and usually stayed for 4 to 8 days. Due to disintegrated red cells and more fiber content of the lung, it will appear grayer or paler. At this stage, there will be a decrease in blood flow to the lung so this stage is called an avascular stage. At this stage, symptoms start to resolve.


This stage occurs after 8 days where fibers and other debris in the lung will be resolved. The debris either reabsorbed or ingested by the immune system or coughed up. So at this stage, there will be a productive cough which will remove the debris from the lung.

So these are the 4 stages of pneumonia. And it is important to know the stages because the sooner you seek a medical attention, the better the prognosis will be. So make sure to contact your doctor if you experience fever, shortness of breath and cough.

Watch this video to know more about pneumonia.

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