Understanding what affects certain ingredients have on your hair, and why, can help you make your own hair care products and choose the commercial products that will best serve your hair care needs. Let us begin with the most basic and common ingredient, water, and the meanings of the numbers. The Power of Hydrogen scale, better known as pH, measures all materials on a scale from 0 to 14, with 7 being neutral. Pure water is a neutral 7 with anything lower being acidic and anything higher being alkali or a base. Items like hydrochloric acid, which is a 0 in the pH scale, have extremely low amounts of hydrogen bonds within its molecular structure. Lye, which rates a 14 on the pH scale, has an extremely high amount of hydrogen bonds. Our skin and hair generally falls between 4.5 and 5.5 on the pH scale, which makes it as slightly acidic. Bodily fluids, aside from out stomach acids, are alkali.
Now, you might be wondering what this has to do with you, and the ingredients that you put on your hair and skin. Well, here comes what you really want to know. Weak acids, like vinegar which typically runs 2.4 to 3.4 of the pH scale, is applied to your hair it closes your hair cuticles. This in turn will make your hair shinier and softer. Mild acid rinses are also good when trying to return your hair to its natural shape, which can come in handy in releasing a stubborn curl or other heat styling shape such as crimping after the event it was done for is over. If your hair has moderate to extensive damage acidic ingredients can dry out your hair a little. However, that effect can be counteracted by diluting the acid a fair bit. It is also said that an acidic rinse can help relieve dandruff. Acids can also good for removing some kinds of build-up, such as soap scum. However, acidic rinses cannot help remove silicone, and other chemical build-ups, from commercial hair products. Using an all-natural acidic rinse including lemon juice, lime juice or vinegar can do wonderful things for your hair. Recipes for such rinses often include fragrant herbs as well as those with properties that can further enhance your hair. One of the most basic rinses that I use simply uses four teaspoons of water, two teaspoons of apple cider vinegar and three drops of lemon essential oil for each rinse. When adding herbs or essential oils, remember that less is always more with essential oils and herbs so start off with one drop, my most common additions to acidic rinses include rosemary, lemongrass and peppermint.
When alkali ingredients are applied to the hair, it has an effect that leans in the other direction. Instead of closing of the cuticles, they open up the cuticles, which can make the hair look dull and feel a little rough. Alkali ingredients are often used in commercial dyes and bleaches to help apply or remove colors. Alkalis are also used in solutions used to perm or relax hair. But this is far from all you need to know in order to do the best for your hair. Strong alkali ingredients, such as lye (Sodium Hydroxide), can do even more to your hair. For instance, if your hair is curly an alkali will straighten your hair a little. Therefore, if you are losing your curl, you might want to switch your shampoo or do an acid rinse to preserve your full curl. Perms, which are essentially the same thing as relaxer at least chemically though obviously not cosmetically. The only difference between using a perm and a relaxer is the shape you are hoping to force your hair to take. With perms you roll the hair and apply a solution, while with relaxers, you brush your hair back and apply the relaxer in order to straighten hair.
Other ways of closing the cuticle, aside from using acidic ingredients, include using soft water or a final cold-water rinse. The most ideal rinse for hair, at least before all the environmental issues of today, is rainwater. Rainwater, without the environmental impurities, was slightly acidic with a pH around 5.5. That slight leaning towards being acidic which would benefit hair and skin and is naturally the softest water, because of the minerals present within the water. If you had hair that was untreated and undamaged by chemicals and the environment and consistently showered with pure, cold, rainwater and we did everything else hair conscious individuals should be doing, your hair would be absolutely breathtaking!
Sources:
Hair Crazy, pH and Hair
Virtual Chem Book, pH Scale