Final answer:
Sebum is the oily secretion that lubricates the skin and hair, produced by sebaceous glands, which also has antibacterial properties and prevents water loss.
Step-by-step explanation:
The oily secretion that lubricates the skin and preserves the softness of the hair is called sebum. This substance is produced by sebaceous glands which are located in the dermis of the skin. Sebum is essential for maintaining the health of the skin and hair; it acts as a waterproofing agent, preventing water loss from the skin, and has antibacterial properties that inhibit the growth of microorganisms. Additionally, it keeps the keratinized cells of the stratum corneum pliable. Sebaceous glands are associated with hair follicles and the secretion of sebum increases during puberty due to hormonal stimulation.