What underlying mechanism explains why skin oils can effectively prevent pathogen entry into the body?

Skin oils, mainly sebum, coat the skin surface and form a slick, hydrophobic film that makes it hard for microbes to stick and grow. This oily layer traps water, lowering the moisture available for bacteria and fungi, and its acidity (pH 4–5) inhibits many pathogens that prefer neutral pH. Because the oil is non‑polar, it also blocks the tiny pores through which germs might penetrate, acting like a physical shield. Together, the low moisture, acidic environment, and physical barrier keep most microbes from reaching the skin’s deeper layers. For example, when a hand with a normal oil layer touches a contaminated surface, the oily film prevents bacteria from settling onto the skin, reducing infection risk.