The innate immune system is the body's first line of defense against infections. It consists of various physical barriers, like the skin and mucous membranes, as well as immune cells that respond quickly to invaders. These cells, such as macrophages and neutrophils, recognize and attack pathogens like bacteria and viruses without needing prior exposure. Unlike the adaptive immune system, which develops specific responses over time, the innate immune system acts immediately and broadly. It also includes proteins like complement that help destroy pathogens and signaling molecules called cytokines that alert other immune cells to the presence of an infection.