Washington Esthetician State Board Practice Exam

What serves as the body's first line of defense against infection?

1. Immune system

2. Unbroken skin

3. Mucous membranes

4. Antibodies

The correct answer is: Unbroken skin

The unbroken skin serves as the body's first line of defense against infection because it acts as a physical barrier that prevents pathogens—such as bacteria, viruses, and fungi—from entering the body. Skin is composed of multiple layers, with the outermost epidermis being particularly crucial for this protective function. It contains keratin, which is a tough protein that adds to the barrier properties, and it is also supported by natural oils that can inhibit microbial growth. This protective mechanism is key because, unlike other components of the immune response, which are activated once an infection is already underway, the skin functions proactively by keeping harmful agents out in the first place. While the immune system, mucous membranes, and antibodies also play significant roles in protecting the body from infections, they are part of a secondary response that activates once the skin barrier is breached or once pathogens have entered the body.