The sebaceous glands produce sebum, a material that:

• A. Causes hair to stand erect when you are cold
• B. Discharges sweat onto the skin's surface
• C. Facilitates shedding of the epidermis
• D. Waterproofs the skin and keeps it supple

Answer: (D)

Sebaceous glands produce an oily substance that coats and protects the skin and hair. This sebum forms a waterproof film and keeps the skin flexible, helping to prevent dryness and cracking. The waterproofing and lubrication effects are what make this option the best description of sebum’s role. In contrast, hair standing up is caused by tiny muscles at the hair follicle (not the sebaceous glands), sweating is done by sweat glands, and shedding of the epidermis is part of skin turnover rather than sebum activity.