Endotoxin is a toxic substance found in the outer membrane of certain bacteria, particularly Gram-negative bacteria. It is composed of lipopolysaccharides and is released when the bacteria die or multiply. Endotoxins can trigger strong immune responses in humans and animals, leading to symptoms such as fever, inflammation, and in severe cases, septic shock. Endotoxins are important in medical and research settings, as they can affect the safety of pharmaceuticals and medical devices. Testing for endotoxin levels is crucial to ensure that products are free from contamination, as exposure can pose serious health risks to patients and individuals.