What is sepsis?: NASCAR champion Kyle Busch's sudden death from severe pneumonia progressing to sepsis has sparked widespread concern. The article explains how pneumonia, an infection filling lungs with fluid, can trigger a dangerous immune response leading to sepsis, where the body attacks itself. Early recognition and treatment are crucial to prevent life-threatening complications.

Kyle Busch's cause of death has not been given, though his family said earlier the NASCAR icon had been hospitalized with a "severe illness."

Fans continue to mourn Kyle Busch two days after the NASCAR legend's sudden and shocking death at age 41. Here's what we know.

Busch, a two-time NASCAR champion, died at 41 on Thursday

Kyle Busch died after severe pneumonia progressed into sepsis, leading to rapid complications.