There are numerous causes of oily hair and skin. Typically, one is not associated with the other (meaning that the causes of oily hair and the causes of oily skin often differ). However, sometimes there is an overlap, especially when the cause is diet or hydration deficiency. Most causes of oily hair and skin are easily treated with cosmetic products or proper washing.
Oily Hair Causes
Oily hair is commonly caused by genetics and certain individuals are more prone to oily hair than others. This is especially true during puberty, when the hormones cause a higher production of sebum. Sebum is a waxy-type substance that occurs in the body and is meant to keep hair waterproof. As a result, it becomes more difficult to properly wash substances out of hair, leading to a more oily feeling in the hair. Additionally, while regular washing of hair is recommended, excessive product use may be detrimental and lead to an oily build-up. The best way to deal with oily hair is to wash your hair regularly, at least once every other day, and use the recommended amount of products as prescribed by a physician.
Oily Skin Causes
Oily skin is also caused by a build up of sebum, especially during puberty. Oily skin can also be the result of exercise or large amounts of sweating, which can result in an increase of sebum production. Unlike oily hair, oily skin is a bit more difficult to cure because dry skin is considered as bad as oily skin. The best way to clean oily skin is to used a mild detergent with no oil in it. Avoid using moisturisers and oil-based sunscreens if you commonly suffer from oily skin.
Deficiencies in Diet
Both oily skin and hair can be exasperated by certain a lack of certain foods in a diet. Essential fatty acids--found in salmon, walnut and flaxseeds--help promote healthy skin and hair growth, and thus can be a factor in preventing excessive oiliness. Same for Vitamin A--found in many dairy products--which acts as an antioxidant. Finally, a high-level of water consumption allows for both plant and skin cells to remain hydrated, and thus help cleanse the skin of excessive oils.