They secrete an oily substance called sebum which:
* Moisturizes the skin: This prevents the skin from drying out and becoming cracked or flaky.
* Lubricates the hair: Sebum coats the hair shaft, making it smooth, shiny, and less prone to breakage.
* Protects the skin: Sebum creates a protective barrier on the skin's surface, helping to prevent water loss and protect against bacteria and fungi.