Exotoxins are toxic substances secreted by bacteria into their surrounding environment. These proteins can cause damage to host cells and tissues, leading to various diseases. Common examples of bacteria that produce exotoxins include Staphylococcus aureus and Clostridium botulinum. Unlike endotoxins, which are part of the bacterial cell wall and released only when the bacteria die, exotoxins are actively secreted during bacterial growth. They can trigger strong immune responses and may be used in vaccines, such as the diphtheria vaccine, to help the body recognize and fight off infections.