Which body system serves as a barrier to foreign substances?

The integumentary system serves as a barrier to foreign substances, primarily through the skin, which is the body's first line of defense. The skin acts as a physical barrier that prevents the entry of pathogens, chemicals, and other harmful substances. It also contains various cells that can detect and respond to potential threats, enhancing the immune response.

Additionally, the integumentary system plays a crucial role in other protective functions, such as regulating temperature and providing sensory information. The presence of sweat and sebaceous glands also contributes to the barrier function by creating an environment that is less hospitable to pathogens. This makes the integumentary system vital for maintaining overall health and protecting the body from infection.