You step outside on a chilly morning with wet hair, and your friend warns you to put on a hat to avoid getting sick. Which innate immune defense is primarily being described in this scenario, and how does it function as a protective mechanism against pathogens?

The friend is pointing to the skin’s physical barrier, the first line of the innate immune system. When the skin stays dry and intact, it stops bacteria and viruses from slipping in through tiny openings. A wet, chilled hair can compromise that barrier, making it easier for germs to penetrate. By keeping the hair dry and covered with a hat, you help the skin stay strong and keep microbes out.