What is the substance that is secreted by the oil glands?

The substance secreted by the oil glands, known as sebaceous glands, is sebum. Sebum is an oily, waxy substance that helps to moisturize and protect the skin and hair. It plays a crucial role in maintaining skin barrier function, preventing dryness and providing some antibacterial properties. By coating the surface of the skin, sebum can also help to reduce water loss, keeping the skin hydrated.

Collagen and keratin are two proteins found in the skin and hair. Collagen is responsible for skin structure and firmness, while keratin is a structural protein that aids in the formation of the outer layer of the skin, hair, and nails. Hormones are signaling molecules in the body that regulate various processes, including the functioning of oil glands, but they are not the substances produced by these glands. Thus, sebum is specifically the correct answer, as it is the direct product of the oil glands.