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What are the 4 Stages of Pneumonia? Find Out Here

Medically reviewed by Mae Charisse Antalan, MD · General Practitioner

Written by Amable Aguiluz · Updated Feb 16, 2023

What are the 4 Stages of Pneumonia? Find Out Here

What is Pneumonia? What are the 4 Stages of Pneumonia?

Pneumonia is an infection of one or both of the lungs. It causes the air sacs of the lungs to fill up with fluids and/or pus, or purulent material. Affected persons have varying degrees of cough, fever, and shortness of breath or trouble breathing. Pneumonia can be caused by a variety of organisms such as fungi, viruses, and bacteria. Pneumonia progresses through various stages as the condition worsens. What are the 4 stages of pneumonia? Read on to find out.

The signs and symptoms of pneumonia vary, depending on factors such as the type of bacteria involved, the patient’s overall state of health and age, and other considerations. For mild cases, signs and symptoms resemble those of a cold or flu, but hold a longer duration compared to your regular cold or flu illnesses.

Symptoms of any type of pneumonia generally include:

  • Chest pain associated with respiratory functions
  • Varying degrees of cough
  • Fatigue
  • Fever, chills, and profuse sweating
  • Irregular body temperature, which in most cases is lower than average
  • Diarrhea
  • Nausea
  • Vomiting
  • Shortness of breath and difficulty breathing
  • Pneumonia is composed of four stages that have different implications on one’s health. What are the 4 stages of Pneumonia?

    What are the 4 Stages of Pneumonia?

    Before we elaborate on the four stages of pneumonia, please note that these stages don’t always happen within the body of a person with pneumonia. Additionally, it is difficult to relate a symptom with a particular stage as they may overlap.

    Stage 1 – Congestion

    The congestion stage usually occurs around the first 24 hours of becoming infected with pneumonia. During this stage, the body will undergo the process of vascular engorgement. This refers to the swelling of the organs of the vascular system.

    This includes the lungs and capillaries becoming very red, swollen, and congested. This leads to the spread of the infection to the hilum and pleura, which are regions of the lungs.

    The hallmark of the congestion stage is coughing and breathing difficulty resulting in the patient needing to breathe in deeper than usual.

    Stage 2 – Red Hepatization

    What are the 4 Stages of Pneumonia? The red hepatization stage occurs around the second or third day after the congestion stage. At this stage, the lungs become red and airless. Visually, they may resemble your liver. The alveolar capillaries become swollen with blood and the vascular engorgement will persist and at some times worsen.

    The patients’ white and red blood cells, along with any cellular debris, can cause a blockage of the alveoli and the airways, which amplifies the effects and spread of the bacteria.

    Stage 3 – Gray Hepatization

    The third stage, known as gray hepatization, occurs anywhere between the 4th to the 6th day, after the red hepatization stage has ended. The lungs begin to appear gray or brown in color as the blood cells found in or around the lungs begin to disintegrate. The lungs become more damaged as the debris surrounding its airways and air sacs become more fluid-like.

    Stage 4 – Resolution

    The resolution stage, which happens at around the 7th to 10th day, occurs when there is a complete recovery of the lungs and other affected body parts thanks to enzymatic digestion. This occurs by the resorption of accumulated cellular debris and fluid. This leads to the repair of the alveoli and airways. There is a chance of the development of scar tissue during this stage.

    Key Takeaway

    Pneumonia is an infection of the lungs. It causes the air sacs in the lungs to become congested with fluids. It makes breathing difficult, and may also cause chest pains, fever, diarrhea, and nausea.

    The 4 stages of pneumonia include the congestion stage, red hepatization, gray hepatization stage, and resolution.

    When you find yourself experiencing any of the symptoms of pneumonia, make sure to immediately consult with your doctor.

    Learn more about Pneumonia here.


    Hello Health Group does not provide medical advice, diagnosis or treatment.

    Medically reviewed by

    Mae Charisse Antalan, MD

    General Practitioner

    Written by Amable Aguiluz · Updated Feb 16, 2023

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