Skin
The first line of defense against any pathogen attempting to invade the body is your skin. The largest organ of your body can physically prevent invaders from getting inside and can also chemically change them by methods such as sweat and desiccation.
Answer: Skin ;)
Your skin serves as both a physical and chemical barrier against pathogens. ... Sweat acts as a chemical barrier because it contains acids that kill many bacteria. Old skin cells are shed constantly, and the pathogens on these cells are shed too.
