Hair 101

Hair Chemistry

To gain in-depth, clinical knowledge of hair chemistry one must first have knowledge of the pH scale and what it represents. The pH scale is a measure of value for potential hydrogen, for which there are two chemical extremes: acid or alkaline. The scale runs numerically from 0-14, with 7 serving as neutral. A measure of pH 0-6.9 is considered acid, while a measure of 7.1-14 is considered alkaline. As you move toward either extreme (acid toward 0, alkaline toward 14), the more caustic and stronger a substance will become. Substances which are acid have a positive electrical charge (+), while alkaline substances have a negative electrical charge (-).

In a normal, healthy state hair is positively charged and will be found in a pH range between 4.5-5.5. Therefore, we can state that hair, in its optimum state, is acidic. Hair which has a pH above 7 will become alkaline and hold a negative electrical charge. When this occurs, the hair will exhibit damage to varying degrees. Examples of how hair becomes alkaline:

* Natural body chemistry
* Inferior, alkaline-based products
* Chemical solutions (perms, colours, bleaches, etc.)
* Thermal styling appliances (blow dryers, curling irons, hot rollers)

When hair is in its proper pH range (4.5-5.5), the cuticle is compact and constricted. This serves to protect the cortex, impart sheen, align the bonding (optimum configuration for strength and elasticity) and positively charge the hair in preparation for chemical services. In the event the hair is in an alkaline state (above pH 7), the cuticle is raised (tangles, dullness), the cortex is exposed (dryness, damage), and the hair will not readily or evenly accept chemical services.

The proper pH can be attained or maintained by using a low pH product (usually 3.0-3.5; substances below 2.0 are considered caustic). This will reduce alkaline levels and allow the hair to assume a proper pH (4.5-5.5). This process is called acidification, and it is the first and most vital factor in hair chemistry and hair care. Important factors to remember:

* All chemical service solutions are alkaline.
* Distilled water is pH 7.0 (neutral).

Chemical Bonding – The Key to Chemical Services

The hair’s cortex is comprised of smaller microfibers that are held together by four types of chemical bonds: hydrogen bonds, ionic/salt bonds, cystine bonds and polypeptide bonds. Knowledge of how these bonds work in the hair is useful as it relates to chemical servicing.

Hydrogen Bonds
Think of a hydrogen bond in a hair strand this way: a piece of pasta is softened by water, after which its shape may be changed. The pasta may then be allowed to cool and harden into a new shape. This is how a hydrogen bond acts in the hair, with the addition and subtraction of hydrogen. These bonds allow the shape of the hair to be temporarily changed with the aid of water. This bond is responsible for about 35% of hair’s strength, and nearly all of hair’s elasticity. It is the only bond broken down by water.

Ionic/Salt Bonds
Responsible for about 35% of the hair’s strength and is very important in hair colouring because it hosts attachment sites for hair colour.

Cystine Bonds
Responsible for the hair’s toughness or abrasion resistance and is important for successful permanent waving. Effected by all chemicals.

Polypeptide Bonds
The polypeptide, or sugar bond, holds one amino acid chain to another. The attachment is by positive/acid to negative/alkaline attraction. This is where pH balance, or lack thereof, comes into play.

The combined force of these four bonds creates hair’s tensile strength.