Which substance is secreted by the sebaceous glands in the skin?

The substance secreted by the sebaceous glands in the skin is sebum. Sebaceous glands are specialized glands affiliated with hair follicles, and their primary function is to produce this oily substance. Sebum serves several important purposes: it helps to keep the skin moisturized, prevents the hair from becoming brittle, and provides a degree of waterproofing to the skin, which can protect against external environmental factors.

In contrast, keratin is a protein found in skin, hair, and nails, contributing to their structure and resilience. Sweat is produced by sweat glands, which play a crucial role in thermoregulation and excreting waste. Collagen is a structural protein found in connective tissues throughout the body, including skin, but it is not secreted by sebaceous glands. Understanding the specific roles and origins of these substances is important in the study of human anatomy and physiology, especially in medical and aerospace contexts.