What is the body's first line of defense against disease?

The skin serves as the body's first line of defense against disease due to its role as a protective barrier. It acts as a physical shield, preventing pathogens, such as bacteria and viruses, from entering the body. The skin's structure includes multiple layers that provide both a mechanical and biochemical barrier. For instance, it has a tough outer layer that resists penetration, while the secretion of oils and sweat creates an environment that is less conducive to pathogen growth.

Furthermore, the skin is equipped with specialized cells that can recognize and respond to potential threats. These include cells involved in the immune response that can detect and alert the body to the presence of harmful invaders. This initial defense mechanism is crucial for maintaining overall health, as it helps to prevent infection before it can spread or cause illness.

Other systems like the immune system, respiratory system, and digestive system play significant roles in the body's defense against disease, but they operate as part of secondary responses once a pathogen has breached the skin barrier.