What organ serves as the first line of physical defense against infection?

The skin serves as the first line of physical defense against infection. Here's a step-by-step explanation:

1. The skin is the largest organ of the human body. It covers and protects the body's underlying tissues and organs.

2. The outermost layer of the skin, known as the epidermis, serves as a physical barrier against harmful substances, including bacteria, viruses, and other potential pathogens.

3. The skin is also coated with a layer of natural oils that contain antimicrobial substances, further enhancing its defensive capabilities.

4. In addition to its physical barrier function, the skin also has immune cells that can recognize and fight against infections.

5. If the skin is broken or damaged, it can be more susceptible to infections. However, the skin also has the ability to repair itself, which helps maintain its role as a protective barrier.

So, the skin is the organ that serves as the first line of physical defense against infection.