Which substance is secreted by the sebaceous gland?

The substance that is secreted by the sebaceous gland is sebum. Sebum is an oily substance that plays a crucial role in maintaining the health of the skin and hair. It acts as a natural moisturizer, helping to prevent dryness and maintaining the skin's barrier function. This oily secretion is composed of various lipids, including triglycerides, wax esters, and squalene, which help to lubricate the skin and hair, giving them a healthy appearance.

The other options, while important components of skin health, are not produced by the sebaceous gland. Keratin is a protein that forms the structure of hair, skin, and nails, providing strength and resilience. Melanin is the pigment responsible for skin, hair, and eye color and is produced by melanocytes, not sebaceous glands. Collagen is a protein that provides structural support in the skin and connective tissues, but it is synthesized by fibroblasts.

Understanding the role of sebum and the function of the sebaceous gland is important for skin care and addressing issues related to oiliness or dryness in the skin.