What structure in the skin produces oil to protect the skin and hair from drying?

The sebaceous gland is responsible for producing oil, known as sebum, which plays a crucial role in protecting both the skin and hair from drying out. This oil helps to lubricate the skin and hair, maintaining moisture and preventing water loss. Sebum also has antimicrobial properties, which can help protect the skin from infections. The presence of sebaceous glands is particularly notable in areas rich in hair follicles, as they secrete their oil directly into the hair follicle.

In contrast, sweat glands are primarily involved in thermoregulation and waste excretion through the secretion of sweat, rather than providing moisture to the skin and hair. Hair follicles are structures that house the hair but do not produce oil; they are involved in hair growth. Keratinocytes are the predominant cell type in the outer layer of skin and are responsible for the production of keratin, which contributes to the skin's barrier function but does not produce oil. Thus, the sebaceous gland is the correct answer, as it specifically provides the oil necessary to protect and moisturize the skin and hair.