Answer:
Skin
Step-by-step explanation:
Your skin is a barrier. The top layer of skin is made up of cells that are packed in a tight, overlapping pattern. Lipids that your body produces seal the tiny space between the cells, creating a barrier that's essentially waterproof and pathogens-proof. When pathogens such as bacteria or viruses land on your skin, they simply cannot enter your body.
Your skin also secretes several substances that help kill pathogens. Sweat, for example, does a lot more than keep you cool on a hot day. It contains an enzyme that breaks down bacterial cells. And, your skin's surface is naturally somewhat acidic, which prevents many types of pathogens from growing.