The idea of what is "clean" has changed a lot over the centuries. Today we attempt to wipe out organisms we can't even see! Obviously visible dirt, odor, and etiquette are still the defining factors as we go back. I'm going to use 18th century Anglo society as the example, simple because it's close enough in time that you'll see some carry over, but so much of the drastic change occurred in the late 19th century that much will be unfamiliar. If you want a long overview of other times I recommend The Dirt On Clean: An Unsanitzed History.

The most common method of keeping the body clean at this time was through use of undergarments. Men's shirts and women's shifts covered the body and created a barrier between them and their outer clothing. A shirt goes around the neck, down to the wrists, and would have hung to about the knees before being tucked between the legs and the breeches pulled on. A shift has a lower neckline, mirroring that of gowns, the sleeves go to around the elbow (also mirroring gowns), and the length is usually about mid-calf. Most often made from linen, these will absorb a lot of oil and sweat. Linen is breathable, wicks away moisture, evaporates easily, and is slightly anti-microbial so it won't stink as easily. Wool has similar attributes aside from the "cool" feeling of linen, used in very cold climates instead. This undergarment is worn for a day at most, recommendations are to change it multiple times if it is hot or the person is sweating greatly. It's then boiled, washed with lye soap, or even bleached to return it to a clean white. Eventually the collars, cuffs, and even the gussets under the arms will wear, stain, or rot and be replaced. These garments are mass produced by this time in England and are bought in packages of 6 or 12 at an affordable price. I feel it necessary to note at this point that I (and other people I know) have tried this method and it works surprisingly well. 86-93% of what comes off of your body goes into your clothing, the rest in the shower according to this study.

Washing is also done regularly, though not whole body submerged bathing (note that showers are not technically "baths" either by definition). So, when someone mentions they only bathe once or twice a year, it's specific to getting into a large basin of water. Something that is very difficult to heat properly, as well as supply with that quantity of water prior to running water in the home. Most washing is done from a basin with castille soap. London, as well as numerous places in France, had a large soap making industry from the 16th century. It was recommended to wash the face only with cold water, but the hands and other body parts "as necessary" were washed with soap as well. This was a nightly ritual, for some in the morning as well, and washing hands was done before meals.Grooming kits, oils and essences, tooth brushes and powders, and all sorts of other familiar items can be found in the 18th century as well. A great quote from Hannah Wooley (lived 1622-1675): For stench under arm-holes, first pluck away the hairs of the armhole and wash them well with white wine and rosewater wherein you have boiled cassia lignum (an aromatic bark).

Now, hair, for that is a very different process. I'm not looking for a written answer, just for you to think about this. How long is your hair and how did you wear it between washes? If you wore it down or even uncovered than you'll be exposing it to a great deal of outside dust, dirt, and smells that create the need to wash your hair much more often. This is why the 18th century woman often wore a cap, outside of the "no bad hair days" benefit. In a world with fires in every home year round for cooking, dirt roads, open windows, and no air filters the hair would have been covered in grease, dirt, and dust very quickly when working. The actual haircare and cleaning process consisted of pomade and powder. Think of them like a dry shampoo and conditioner. The pomade is fat based, with varying oils and scents. Clove oil was very popular and is actually a natural insect repellant. Add in that lice and such like very clean hair, so the myth of insect-ridden hair is just nonsense. After combing pomade through the hair, the powder is applied. This too is often scented with things like oris root and can be tinted to match the hair better (or in pink or lavender, etc). This absorbs the greasy feeling from the pomade and makes the hair extremely full and easy to style. From there it can be put up under a cap or styled over cushions and rollers (or both). The finished styled hair will often be powdered more to finish it, though the amount is up to personal preference. The style will be taken down each night, though the pomade/powder process only needs to happen every few weeks with powdering as need be to avoid oil (much like the dry shampoos today). Vigorous combing is also recommended to prevent scalp build up. Brushing and combing the oils through the hair makes a big difference, though a boar bristle brush is needed for it to actually work well. Again, this is something I and others I know have tested out and it does work. It does look a little weird to the modern eye, but it doesn't smell bad or feel dirty. It did take me six months of gradually washing less to get to the point where I can go a week without regular washing if not doing pomade/powder. And not using regular shampoos or it'll shock the scalp into overproducing oil. It's a hard process to reverse.

As I mentioned earlier, so much of our "modern" process for cleaning our bodies was developed and heavily advertised in the late 19th/early 20th century. The idea that you weren't beautiful unless you were "clean" was a huge marketing tactic that is still used today. If that person you're talking to smells any body odor, or sees a stain on your clothing, or notices dirt under your nails it's just the worst thing ever. The commercials convinced us of this on both sides, not only being determined that we will clean neurotically to make sure that doesn't happen, but now judging those that don't follow that concept. Most of our tools for this aren't new, but they have been re-developed to be more effective and attractive.

There's always room for discussion, but perhaps the section Health, Hygiene, & Personal Grooming in our FAQ will answer your inquiry.