Final answer:
The skin acts as a mechanical barrier against pathogens through a layer of dead, keratinized epidermal cells that are constantly shedding, along with acidic and lipid-containing secretions that inhibit pathogen survival.
Step-by-step explanation:
The skin is a critical component of the body's defense system, offering a substantial barrier against various pathogens. The principal mechanism by which the skin protects against diseases is through acting as a mechanical barrier. This barrier is formed primarily by an outer layer of epidermal cells made up of dead, keratinized epithelium. Not only is this layer too dry for bacteria to grow, but it constantly replaces itself, shedding off the surface along with any pathogens that may have adhered to it. Additionally, secretions from the skin, such as sweat, can lower the pH and have toxic lipids that contribute to its protective function by directly killing or inactivating pathogens, further preventing infections. As for the hair follicles, they serve as accessory organs, trapping larger pathogens before they can enter the body.