The death of NASCAR champion Kyle Busch has drawn attention to the rapid and devastating complications that can result when pneumonia advances to sepsis, doctors say.

Busch, a two-time Cup Series champion, died Thursday at the age of 41 after a brief hospitalization for what his family described as a “severe illness.”

In a statement released Saturday, the Busch family confirmed that “severe pneumonia progressed into sepsis, resulting in rapid and overwhelming associated complications,” according to a report shared by FOX Sports journalist Bob Pockrass.

Fox News senior medical analyst Dr. Marc Siegel explained that Busch’s case demonstrates how a lung infection can swiftly overwhelm the body if it spreads into the bloodstream.

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Busch reportedly developed a sinus infection that worsened prior to his death. “This upper respiratory sinus infection progressed to pneumonia,” Siegel told Fox News Digital.

Pneumonia is an infection that fills the lungs with fluid, making it difficult to breathe. The condition can be caused by bacteria, viruses, or fungi, and symptoms often include fever, chills, cough, chest pain, and shortness of breath.

Siegel noted that bacterial pneumonia is usually more severe than viral forms.

He added that physical strain — such as the G-forces simulated by racing training equipment used by professional drivers — might aggravate inflamed lungs during recovery, though he emphasized that direct evidence remains limited.

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Once an infection spreads from the lungs into the bloodstream, sepsis can occur. Sepsis is a life-threatening condition caused by a widespread inflammatory response that can damage tissues and organs.

“The body reacts to this severe lung infection by making inflammatory chemicals. It’s the immune system revving up,” Siegel said. “But as with a lot of things with the body, the immune system can hurt more than help.”

As sepsis advances, blood pressure can drop, and oxygen delivery throughout the body becomes impaired. Siegel explained that this can trigger lactic acidosis, a buildup of lactic acid in the bloodstream that further disrupts organ function.

“The kidneys fail, toxins from the kidneys build up, blood pressure goes down, fever goes up, the lungs fail — something called ARDS,” Siegel said, referring to acute respiratory distress syndrome.

ARDS occurs when inflammation causes fluid to leak into the lungs, preventing oxygen from reaching the bloodstream. It is one of the most severe complications of sepsis and is often associated with critical illness.

The Centers for Disease Control and Prevention lists possible warning signs of sepsis as confusion, rapid breathing, extreme weakness, bluish or mottled skin, low blood pressure, and a fast heart rate.

Doctors emphasize that sepsis is always a medical emergency because patients can decline rapidly within hours if not treated promptly.

Those most at risk include older adults, smokers, and people with chronic lung disease, diabetes, weakened immune systems, or recent viral infections.

Busch’s death has left the NASCAR community in mourning while also serving as a stark reminder of how quickly common respiratory illnesses can turn life-threatening.