How often should you wash your hair?

With all of the sebum excreted onto our hair and skin, it's no wonder why we love to shampoo. See more pictures of personal hygiene practices.
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You've had your sebaceous glands for some time now -- for your entire life, actually. They began to appear beneath your skin during your fourth month in the womb and are found in their highest concentration along your scalp and face, although they are found everywhere on your body except for the palms of your hands and the soles of your feet.

These glands are usually connected to an individual hair follicle (except on hairless places like your eyelids and lips, where they work alone). Now that you know what they are and how they formed, you might want to know what they do. Sebaceous glands are responsible for secreting sebum, the natural oils that moisturize and waterproof your skin and hair. Deep in the skin's dermal layer, specialized secretory cells that absorb fats from the body enter the sebaceous gland and disintegrate. At this point, these cells become sebum. The sebum is expressed into the lumen (shaft) of the hair follicle, where it's excreted up to the skin's outer layer, the stratum corneum. In other words, your body burps excreted fats and cellular debris onto your skin and hair.


No wonder we use shampoo.

As gross as it sounds, it provides a necessary function. As we've seen, sebum waterproofs and moisturizes your skin and hair. Without this stuff, the skin can dry and shed prematurely, leaving thriving cells exposed to the elements. But isn't allowing sebum to accumulate on our hair and skin the same as being unwashed and oily? In modern Western culture, it certainly is.

Our bathing and hair washing routines are based on a strange system of depleting the skin and hair of their natural oils by lathering up with soap and shampoo and then replenishing them with moisturizers and conditioners. We carry out this (usually) daily ritual for a couple of reasons: By Western standards, the appearance of oily, unwashed hair is generally unacceptable -- and it just feels kind of gross to go without a bath or shower for more than a couple of days. Secondly, these natural oils can lead skin conditions like acne vulgaris, where sebum becomes backed up in the hair follicles, creating a smorgasbord for bacteria, which break the fats into fatty acids. These create an allergic reaction that presents itself as acne.

For more information about hair washing, read Hair Washing: Fast Facts.

But if there are benefits and drawbacks to both washing and not washing your hair, it seems like there's a balance to be struck. How often should you wash your hair, exactly?


To Shampoo or Not to Shampoo?

50s hairdresser
In the mid-20th century shampooing was a weekly endeavor left to hairdressers.
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So you want to maintain your status as an acceptably non-smelly member of society. Good for you. Where does this leave you? How often should you wash your hair?

It turns out the answer to that question is based on personal preference. Even among medical professionals that specialize in the skin, hair and scalp -- dermatologists and trichologists -- there's disagreement about the usefulness of shampooing and just how frequently one should use shampoo, if at all. Some advise against frequent shampooing, pointing out it leads to overproduction of sebum to compensate for its constant removal [source: Aubrey]. Others say shampooing is necessary to prevent sebum from collecting in the pores and hair follicles and leading to skin problems like acne [source: Grossman].


The concept of daily home shampooing is a relatively new one. Back in the 1950s, it was common for women to have their hair washed and styled once a week at the hairdresser. These folks got by just fine, and the trend has made a resurgence in recent years as more salons report clients that have chosen to shift shampooing to a weekly rather than daily ritual [source: Grossman].

Around the turn of the 20th century, women tended to go for about a month between salon visits. A 1908 advice column in The New York Times, however, helped usher in a sea change in shampoo usage when it told readers that shampooing every two weeks is perfectly acceptable [source: Aubrey].

Others have learned to postpone shampooing for even longer periods. An uncontrolled and impromptu study of the effects of going without shampoo was inadvertently launched in 2007 when a guest on an Australian radio show mentioned he hadn't washed his hair in a decade. After calls to the show came in, a six-week challenge was issued and 500 listeners participated. After six weeks of going without shampoo, 86 percent of the respondents reported their hair was no worse or better than it was when they used shampoo regularly [source: Lacko].

Others use different means to keep their hair clean. Dry powder products are available on the market that absorb some of the natural oils. The remnants are removed by blotting with cheesecloth and combed out [source: Grossman]. Baking soda also serves a similar purpose. Coupled with a raw egg and a final rinse with lemon juice, it provides an all-natural hair cleaning regimen [source: Siegle].


Lots More Information

Related HowStuffWorks Articles

  • Aubrey, Allison. "When it comes to shampoo, less is more." NPR. March 19, 2009.
  • Bunn, Bill. "What's really in your shampoo." Salon. August 13, 2009.
  • Encyclopaedia Brittainica. "Sebaceous glands." Accessed September 24, 2009.
  • Eroschenko, Victor P., et al. "Di Fiore's atlas of histology of functional correlations." Lippincott Williams & Wilkins, Ninth Edition, 2000.
  • Grossman, Anna Jane. "Of course I washed my hair last year (I'm almost certain)." New York Times. February 21, 2008.
  • Lacko, Rebecca. "Green living 101: How often should I wash my hair?" July 26, 2009.
  • Siegle, Lucy. "Should I stop washing my hair?" The Guardian. July 2, 2006.
  • Random History. "The innovation of shampoo: a culmination of personal cleanliness." July 19, 2008.
  • Washington Suburban Sanitary Commission. "Water usage chart." Accessed September 24, 2009.