Sebum or oil is generally demonised and made out to be the bad guy when you have acne. People give you advice on how to wash your face multiple times a day so that you can wash off the oil. There are face washes and moisturisers and foundations all with labels that say oil-free. These are targeted at people who have acne. If you have acne you are told to stay away from any hint of oil in your skin care.
What is Sebum
Sebum is an oily substance produced by your skin’s sebaceous or oil glands. Sebum in Latin means fat. It is made up of triglycerides, wax esters, squalene, and free fatty acids. Testosterone stimulates the production of sebum while estrogen inhibits it. Source
How Many Sebaceous Glands Do You Have
You have sebaceous glands all over your body, except the palms of your hands and the soles of your feet. The number of sebaceous glands in your face, scalp, chest, upper back and shoulders are more in number than anywhere else on your body. You can have as many as 400-900 glands per square cm of your face. The gland is either attached to a hair follicle or found on its own. Source
This is the reason why you are more likely to get acne on your face than anywhere else on your body. You just have more sebaceous glands on your face, than anywhere else. Remember those Chinese Face Maps that tell you that acne on a certain part of your face must be linked to your liver? Those are all made up. The simple reason that you get acne on your face is because of the number of sebaceous glands on your face.