Final answer:
Sebum is the material secreted into hair follicles to waterproof and lubricate the skin, produced by sebaceous glands.
Step-by-step explanation:
The material that is secreted into hair follicles to waterproof and lubricate the skin is called sebum. Sebum is produced by sebaceous glands, which are exocrine glands found all over the body, though not on the palms of the hands or the soles of the feet.
This oily substance not only helps to prevent water loss from the skin but also has antibacterial properties, inhibiting the growth of microorganisms on the skin. Sweat glands, on the other hand, produce sweat, which is a salty fluid for thermoregulation, rather than lubrication and waterproofing.