What role do the skin and mucous membranes play in the immune system?

The skin and mucous membranes play a crucial role in the immune system primarily by serving as physical barriers that prevent the entry of pathogens into the body. The skin acts as the body's first line of defense, providing a tough, protective layer that is difficult for microorganisms to penetrate. It also has innate antimicrobial properties, including the production of antimicrobial peptides and the secretion of sweat and oils that create an environment inhospitable to many pathogens.

Mucous membranes line various body cavities and organs, such as the respiratory and gastrointestinal tracts, and they produce mucus that traps pathogens and particles. Cilia present in some mucous membranes help to transport trapped pathogens out of the body. This physical barrier is complemented by other factors, such as the presence of normal flora that can outcompete harmful pathogens for resources and space.

By preventing pathogens from entering the body, the skin and mucous membranes reduce the likelihood of infection and play an essential role in the overall immune response, allowing the body to mount a defense only when needed.