What is the main substance secreted by sebaceous glands?

Sebaceous glands primarily secrete sebum, which is an oily substance made up of lipids. Sebum plays a vital role in maintaining the health of the skin and hair. Its primary functions include providing moisture, creating a protective barrier, and preventing dryness. By lubricating the skin and hair, sebum helps to keep them hydrated and flexible. It also has antibacterial properties that can help protect the skin from infections.

In contrast, sweat is produced by sweat glands to help regulate body temperature; keratin is a fibrous protein essential for the structure of skin, hair, and nails; and melanin is the pigment responsible for skin and hair color and does not pertain to the activity of sebaceous glands. Thus, the secretion of sebum is critical to skin health and demonstrates the unique and specific role of sebaceous glands within the integumentary system.