Few products make the bold, imaginative, and highly delusional claims that shampoos and conditioners do. Almost every brand describes mystical powers that can revitalize, energize, volumize, and therapize hair (and the last two aren’t even real words).
Unfortunately, the science of hair pours some distinctly unsudsy water on the whole idea. Because each one of your hairs is a sorry strand of dead material, there’s really nothing you can do to “nourish” it. That means you don’t need to shampoo with vitamins or amino acids. The best botanicals are the ones you grow in pots and water twice a week, and you’re better off rubbing herbs and fruit extracts on your dinner than on your scalp.
And forget other hair-care health claims—the government doesn’t regulate shampoo, so manufacturers don’t need to substantiate their fanciful promises. (For example, some shampoos boast that they protect hair from ultraviolet rays. This typically means that the manufacturer has added a UV-protective ingredient, which you’ll only end up rinsing down the drain, and which isn’t present in strong enough concentrations to have an effect in the first place.)
The truth of the matter is that shampoo provides a rather straightforward hair-cleaning service. To understand how it works, you need to know how your hair gets dirty in the first place. Ordinarily, the same sebum that lubricates your skin moisturizes your hair. This is mostly a good thing, because the thin layer of oil protects your hair from damage. But as the hours pass and you go about your daily business, your hair collects natural oil and skin flakes that shed from your scalp. This is where shampoo comes in—it includes powerful surfactants that dissolve these substances, in much the same way that you rinse dirt out of clothes with detergent or grease out of pots with dish soap. The problem is that, in the process, shampoo strips out most of the sebum, leaving your hair dry and fragile (although the effect is far gentler than if you showered with laundry detergent or dish soap).
To balance this effect, many shampoos have conditioning agents, and many people use a separate conditioning product. There’s a bit more variability to the way that conditioners work, but essentially they all aim to coat the hair shaft with protective sebum-like compounds. Some creamy conditioners feel heavy in the hair and glue together damaged fibers and loose scales. Other conditioners are lighter and oilier. But all these substances cling to the hair shaft and don’t rinse out with plain water.
The best hair-care advice for a biology wonk is this: Don’t break your budget on high-end products. Buy the shampoo that matches your hair type (oily or dry) and use conditioner to manage excessive dryness. Finally, don’t pressure yourself into washing your hair every day. If you’re just as happy waiting a day or two, your dead hair will probably be a bit better off.
Source of Information : Oreilly - Your Body Missing Manual (08-2009)