The skin produces natural oils, but when we shower, we remove those with water and wiping down. I'm wondering if our bodies adjust to the constant showering by producing oils faster. Sometimes, if I shower every day for a week, and then stop for a day, my head feels like it gets oily faster.
The first synthetic shampoos were introduced in the 1930's and by '70s and '80s, daily shampooing became norm in the US. So shampooing in the modern sense (water to produce a soapy lather) is only about 100 years old.
Our modern shampoos are a combination of surfactants (such as SLS) which dissolve natural oils (sebum) and remove dirt particles. As result, it reduces the natural oils in your hair and scalp making it drier than usual, causing the scalp to produce more oil to compensate.
Michelle Hanjani, a dermatologist at Columbia University explains:
If you wash your hair every day, you're removing the sebum, then the oil glands compensate by producing more oil"
She recommends that patients wash their hair no more than two or three times a week.
In the 2010 book Packing for Mars, Soviet research said2010:
the skin halts its production of sebum—after five to seven days of not bathing
However this could vary greatly from person to person, as some people could respond better to some products with different concentrations of surfactants.
For example if you have "oily hair" you need a higher concentration of SLS to help dissolve the oils, when you have "dry and frizzy hair", it would exacerbate the problem.
In 2007 radio audition, Australian Richard Glover decided to challenge his audience to go without shampoo for six weeks. 86 percent of those who 500 people who participated reported that "their hair was either better or the same"wiki.
A study from 1997 showed a link between excessive oil production and anti-dandruff shampoos containing selenium sulfide.
Study was conducted in 120 men in order to quantify the effect of eight proprietary antidandruff shampoos on sebum flow dynamic.
Two shampoos exhibited a significant effect upon the sebum follicular reservoir, steadily increasing the sebum excretion rate in time. One other product induced a significant decrease in sebum output.
Only a few topical products are known to decrease the sebum output at the skin surface:
Among them, the effect of progesterone, astringents, erythromycin-zinc complex, corticosteroids, and elubiol have been documented.
In 2013, the FDA announced that triclosan was found to affect hormone levels in animalsFDA.
Animal studies have shown that triclosan alters hormone regulation. However, data showing effects in animals don’t always predict effects in humans.
A recent study from 2014 showed that shampooing impact on cortisol levels in human hair:
Chemical processing and frequent shampooing affect cortisol levels measured in hair. Chemically processed or excessively shampooed hair should be avoided when recruiting subjects for hair cortisol studies.
Based on above it seems that chemical properties in modern shampoos can affect our hormones, however more studies needs to be conducted to see how exactly it affects our natural oil production (sebum).
To complete the answer of kenorb, I would like to add the second part
According to the America Academy of Dermatology, the number one tip to prevent dry skin is:
Prevent baths and showers
The Great Unwashed, The New York Times explains further:
[...] researchers have discovered that just as the gut contains good bacteria that help it run more efficiently, so does our skin brim with beneficial germs that we might not want to wash down the drain. “Good bacteria are educating your own skin cells to make your own antibiotics,” said Dr. Richard Gallo, chief of the dermatology division at the University of California, San Diego, and “they produce their own antibiotics that kills off bad bacteria.”
Some people have long complained that showering too much makes their skin drier or more prone to flare-ups of, say, eczema, and Dr. Gallo said that scientists are just beginning to understand why. “It’s not just removing the lipids and oils on your skin that’s drying it out,” he said. It could be “removing some of the good bacteria that help maintain a healthy balance of skin."
There is a note:
But Elaine Larson, a professor at the Columbia University School of Nursing with a Ph.D. in epidemiology, cautioned that subway riders, gymgoers and others who come into contact with many strangers should consider soaping up. “If it’s cold and flu season, you want to get rid of the stuff that isn’t a part of your own normal germs,” she said.
If you are about to think that not shower/bath because it's make your skin dry, there are other reasons to reconsider. According to Medical Daily, there is 7 reasons to take a cool shower:
- Increases Alertness
- “Seal” the pores in the skin and scalp
- Improves Immunity and Circulation
- Stimulates Weight Loss
- Speeds Up Muscle Soreness and Recovery
- Eases Stress