An endotoxin is a lipopolysaccharide (LPS) found in the outer cell membrane of gram-negative bacteria. It is considered as one of the most potent toxins and a strong pyrogen (fever- causing substances), which induces various biological reactions when even a small amount of pg (10-12 g) or ng (10-9 g) enters the bloodstream. 

A large enough dose of endotoxin can lead to lung and kidney failure, intravascular coagulation, and a systemic inflammatory response that can lead to septic shock and death.