An excessively oily scalp is usually caused by overactive sebaceous glands, a hormonal imbalance, disease or over-brushing. The scalp can also appear excessively oily if the hair is not washed often enough or if moisturizing shampoos and conditioners are used.
Sometimes the sebaceous glands simply produce too much oil, a condition known as seborrhea. Seborrheic dermatitis causes seborrhea. This overproduction of oil sometimes results in a scaly scalp, greasy crusts on the scalp and even inflammation on the skin. If the condition is extreme enough, prescription shampoo may be necessary.
Androgen hormones control the production of sebum, so a hormonal imbalance often leads to over-production. This is common in teenagers, especially teen boys, because androgens are associated with males. Such hormonal imbalances can also occur during pregnancy. Similarly, diseases that affect the pituitary or adrenal glands or the ovaries can cause increased sebum production.
If the hair is not washed well enough, or if over-moisturizing products are used, the scalp sometimes appears oily. People prone to an oily scalp should wash their hair daily using products especially formulated for this hair type. Scalp toners are another option because they remove excess oil.
Excess brushing can also make the hair look oily. The brush takes the natural oil from the scalp and distributes it throughout the hair. If the brush is used on the scalp, it can even stimulate the production of oil because it stimulates the area as a whole.