What does sebum do?

Despite common belief, that oily, waxy substance on your skin and scalp is actually part of a crucial component to your skin barrier. It's called sebum. Note, some of the oil on your skin could be from sweat and other environmental build up, but the naturally forming secretion is actually incredibly important.

Sebum is a mixture of fatty acids, sugars, waxes and other natural ingredients produced in the sebaceous gland. It forms a protective barrier over your skin to protect and keep it moisturised.  

Sebaceous follicles are found all over the body however more commonly on the face, behind the ears, chest and back. The T Zone actually has the most sebaceous glands which is why this area is more prone to acne. 
Although we aren't exactly aiming for that shine when doing are skincare treatments, sebum does some wonderful things for our skin. It protects and moisturises our skin, helps prevent water loss, improves skin elasticity and provides anti inflammatory and antibacterial benefits. When secreted, it forms a slightly acidic film on the skin which can defend our skin against bacteria, viruses and the like.  Provided you aren't producing too much or too little, a little shine could be the secret to better skin!