After playing outside, Mia notices that her hands feel greasy and she has some dirt under her nails. She remembers her health teacher discussing the body's natural defenses against germs. How does the greasy substance on her skin help protect her from pathogens?

Mia’s greasy skin is coated with sebum, a natural oil that the skin’s sebaceous glands produce. This oily layer fills the tiny gaps between skin cells, making it difficult for bacteria and viruses to slip through and reach the body’s interior. The sebum also contains antimicrobial molecules that can kill or weaken germs that land on the skin. For example, when Mia’s hands touch a dirty surface, the oil on her skin can trap and break down dirt and microbes before they can invade, acting like a sticky, protective shield. Thus, the grease is part of the skin’s first barrier that keeps pathogens out.