I wash my hair with vinegar instead of shampoo. Why?

The original reason was to get away from conventional shampoo that's made from irreplaceable petroleum and weird chemicals.  I was pretty sure it was bad for the environment and possibly for my health.  I'd tried several "earth friendly" shampoos made from plants, but they didn't make my oily hair feel clean, and they still contain a large number of highly processed ingredients, which means that manufacturing them uses a lot of energy.  Vinegar sounded a lot simpler.

Once I started, I was amazed by how well it worked!  My hair looked and felt really nice.  I went to a social event in a smoke-filled bar, but my hair still smelled fresh and clean afterward. 

I had thought I needed leave-in conditioner to make my hair lie down instead of forming a giant frizzball.  I soon learned that the reason I'd "needed" it was that shampoo was stripping too much of the oil from my hair.  Vinegar takes most of the oil off my scalp but lets some of it slide down and coat the hair shafts, like a built-in conditioner.  Vinegar also (I've read) makes tiny scales on the surface of each hair lie flat so that the hair is smoother.

Within a few months, I found that using vinegar meant I could wash my hair much less often!  I'd been washing with shampoo 2 out of 3 days in summer and 1 out of 3 in winter; I now wash with vinegar every 4-7 days in summer and every 7-14 days in winter.  This saves a lot of time and water!  (I wash more often in summer because hot, humid weather makes my hair more oily, while the dry air from winter heating means my hair needs more oil to prevent frizz.)

Disclaimers
I've tested this method only on myself.  My hair is thick, wavy, mid-back length; when I used shampoo, "for oily hair" types worked best; I don't have sensitive skin; I'm of European ancestry.  If any of these factors are different for you, my method may not work right for you, so be prepared to tweak it.

By coincidence, I decided to try vinegar hairwashing at almost the same time I became pregnant.  I have no idea how hormonal changes may have affected the transition process.  All I can say is that I haven't had to change the method much since giving birth.

I wouldn't try this method on a young child because vinegar stings the eyes much more than shampoo, and it's thinner so more likely to get into eyes.

There are many other methods of washing hair without shampoo.  Most use baking soda as well as vinegar, in two separate steps.  Others use lemon juice, honey, or other household substances.  The vinegar-only method works best for me.  (If you search the Web for other ideas, try searching for "no-poo" which is short for "no shampoo"—although it sounds like some kind of weird digestive management!)

Pre-requisite: Learn to rinse your hair.
Although I now wash my hair infrequently, I rinse it every 2 or 3 days.  This really helps to remove dust and lint and such.  It also loosens oil from the scalp and spreads it down the hair shaft.  Getting my hair wet, then air-drying it, reinvigorates the waves.

Daniel deserves credit for explaining to me how to rinse by brushing hair under running water.  (I know, experts say not to brush wet hair.  It doesn't seem to be a problem for Daniel or me.  If your hair is more fragile, use a wide-tooth comb or just run your fingers through it.)  We use a ventilated brush intended for blow-drying; it has slots between rows of bristles, so water runs through the brush.

Rinse with the hottest water you can stand.  First use fingers to lift hair and rub scalp until it's all wet.  Place brush firmly against scalp at front of head and, keeping your head under the shower, pull brush all the way back over your head to the back edge of the scalp, then down the hair to the ends.  Repeat in front-to-back "stripes" until you've done your whole head.

My vinegar washing method
Either white vinegar or apple cider vinegar will work.  Experiment to see which works better on your hair, which smells more tolerable to you while washing, and which leaves less lingering odor in your hair.  White vinegar costs less.  Both types are more affordable in larger jugs.

Put vinegar in a container such as an empty, clean, family-size yogurt tub.  I use about 3/4 cup for my thick, longish hair, and when I add the water (see below) I use about 3 cups.  Optional: Add a drop or two of tea tree essential oil to prevent dandruff.  Set container within reach of shower.

Rinse hair as described above.

Add hot water to the container.  Now you can reduce the temperature and volume of your shower, but it's wise to leave it going a trickle in case you get vinegar in your eyes.

Tip head back and close eyes tightly.  Hold up some hair with fingers, pour a little of the mixture onto your scalp, and rub it in.  Do the same with each area of your head.

Massage scalp and run fingers or brush through hair to distribute oils down the hair shaft.  A lot of the oil will come off onto the shower floor (it's slippery, so watch your step!!) and the rest will coat and condition your hair.

Let it soak for a few minutes while you wash other body parts.  Do NOT shave, as vinegar will sting freshly shaved skin!

Rinse as described above.  Hair will feel slippery and smell vinegary, but these things go away as it dries.

Put damp hair into desired arrangement (barrettes, etc.), scrunch with towel if you like, and let it air-dry.

How to tell when your hair needs washing
You might think this would be obvious, but vinegar-washed hair feels a little different from shampoo-washed hair both when it's clean and when it's dirty, so it takes practice to learn when to wash it again.  Here's how I can tell:

In warm weather, my hair starts to feel sticky and gummy.  It gets difficult to brush, and if I try to braid it there are sections that just won't stay where I put them because they want to form clumps.  If I ignore this feeling for as little as one day, my hair can become so gummy that the brush gets stuck in it.  Time to remove some oil!

In cold weather, my hair becomes less and less willing to lie down.  Either it frizzes, or there are just pieces sticking out straight at odd angles.  Time to move more oil down onto the hair shafts!

The transition from shampoo to vinegar
I started by washing my hair with vinegar every other time, and with my usual shampoo in between.  Right away, I began to feel that my hair didn't get dirty as quickly, so I switched from washing every 3 days to every 4.  Every few weeks I could add another day, until spring turned into summer and I was washing every 7 days.

After about a month, pregnancy nausea was making my usual shampoo smell horrible, so I tried Daniel's plant-based shampoo and found that it now was able to get my hair clean!  (I can't say whether the change had to do with the vinegar washings or with pregnancy.)

After about 5 months, one day I shampooed my hair and it turned out just horrible, very dry and frizzy.  At that point I stopped using shampoo and washed with vinegar every time.

I do use shampoo once in a while.  If my hair feels like it didn't get clean from a vinegar washing and that feeling then gets worse for a couple of days, washing with shampoo will strip off the oil so that my scalp can "reset" and be less gooey.

"But I heard that vinegar is made from petroleum!"
Yeah, I've heard that too: "Be sure to buy Heinz, because those cheap off-brand vinegars are synthetic!"  But in reading labels, I have yet to find a brand that is not made from grain (white vinegar) or apples (cider vinegar).  I often do buy Heinz, because I like to support Pittsburgh-based companies and because their giant-size vinegar at Costco is a good value, but many store brands are made from plants, too—unless their labels are lying and it's all a big conspiracy, that is!