The main cause of the entire problem is the Microscopic Sebaceous Gland which is safely buried under the surface of the skin. They are found in all skin surfaces deep within the dermis. They enter the skin through hair shaft, clear their stuffing through the pores. Most of the oil is produced from the area which contains loads of sebaceous glands which is a part of the pilosebaceous unit. Oily skin can be found on the face in abundance adding forehand, nose and chin. Sebaceous glands contain sebum which has lipids, dead sebaceous gland cells and fats which in return contains triglycerides, wax monoesters, squalane and free fatty acids. Causes of oily skin include:

Heredity
If someone elder than you is going through the same problem in your family, then you can have oily skin problems

Diet
Oily skin can also be caused if you do not take proper diet full of vitamins, nutrition and proteins

Hormone levels
If there is a problem of hormonal imbalance or hormonal shifts, it is also a cause of oily skin. It is common in teenagers and it can happen at any age.

Pregnancy
During pregnancy and menopause, hormonal difference can also disturb the oil balance and increase the production of sebaceous glands.

Birth control pills
Usage in abundance can be Cause of Oily Skin

Cosmetics you use
If you use the cosmetics that do not suit your skin types, then the treatment of Oily skin can be little difficult.