Why Does Hair Become Oily?

If you've ever had to go longer than normal without washing your hair--say, you were camping, or sick--you probably noticed that after a while it begins to look greasy and get weighed down with oil. Everyone's hair has oil in it, but it shows up more quickly in some people than in others.

Normal Oil

Every hair on your body comes out of a hair follicle. In the follicles, along with hair roots, are sebaceous glands. The GirlsHealth website of the U.S. Department of Health and Human Services notes that these glands secrete sebum, an oil that helps keep skin and hair moisturized. This oil can be a good thing: It makes hair look shiny.
Hair care specialist Philip Kingsley, in "The Doctors Book of Home Remedies," links hair type to the number of sebaceous glands. People with fine, light hair have more strands on their heads than people with coarser, darker hair. Redheads usually have fewer hair follicles--80,000 to 90,000--on their scalps, while someone with fine hair might have 140,000. That's 140,000 sebaceous glands pumping out oil.

Puberty

During puberty, the body's hormones are in overdrive, and these include androgens--male hormones--which control the sebaceous glands, Kingsley said. GirlsHealth points out that the common side effect of this is teenage acne, but it can also cause inordinately oily hair. Typically, this phase is temporary.

Genetics

Some people are prone to having oily hair and skin, according to Go Ask Alice, a service of Columbia University. If you are genetically predisposed to oily hair, it will persist throughout your life.

Environment

Heat and humidity can make hair oilier. The website HairBoutique.com adds that some outside factors, such as perspiration, smog, smoke and even too much makeup can make oily hair look even oilier. Using products that aren't designed for your hair type can add to the problem. Go Ask Alice mentions stress and some oral contraceptives as factors that can speed up oil production.

Treatments

There are several things you can do to keep your hair from becoming greasy. Go Ask Alice recommends that you wash it at least daily. The shampoo matters: Pick one designed for oily hair, and give it time to take effect. You may have to try a few brands before you find one that works on your hair. Shampoos with detergents in them are particularly drying, and can help control an oily scalp. When you wash your hair, be gentle when massaging the scalp. Leave the shampoo on for a few minutes before rinsing. A repeat washing may be necessary.
If you must use conditioner, Go Ask Alice recommends one that is oil-free, and says you should apply it only to the ends of the hair, never the scalp. When you comb or brush your hair--which you shouldn't do too frequently--try to stay away from the scalp so as not to stimulate oil production. A mild astringent applied directly to the scalp can help control oil.
If all else fails, a dermatologist can assess your scalp. He may prescribe a treatment that will keep your hair shiny, but not greasy, longer.