Death from pneumonia occurs primarily due to the infection causing severe inflammation and fluid or pus buildup in the lungs' alveoli (tiny air sacs). This buildup impairs oxygen absorption, leading to difficulty breathing and reduced oxygen levels in the blood. The infection can progress to cause complications such as sepsis, where the immune system overreacts and causes widespread organ failure. Additionally, pneumonia can cause blood pressure to drop and the heart rate to increase, destabilizing vital body functions. These cascading effects can lead to respiratory failure, multiple organ failure, and ultimately death. Pneumonia is especially deadly for older adults, very young children, and people with weakened immune systems or underlying health conditions. Infection often advances unnoticed in these populations until severe symptoms like confusion and respiratory distress appear. Without timely and effective treatment, the condition can deteriorate rapidly, resulting in fatal outcomes. Sepsis and acute respiratory distress syndrome are common lethal complications of pneumonia.

In summary, death from pneumonia happens when the lung infection severely impairs oxygen exchange, leads to systemic infection (sepsis), causes organ failure, and disrupts vital body functions, especially in vulnerable individuals. Prompt medical care is essential to prevent these outcomes.