There are essentially three types of hair color: temporary, which lasts only until hair is washed; semi-permanent, which can withstand four to six shampoos before fading; and permanent, which alters the color of the hair until it grows out. Permanent color is by far the most commonly used, accounting for 88 percent of all hair color use, according to research from Procter & Gamble. Because it's so commonly used, many people are curious about the long-term effects of permanent hair color.
There are two different types of permanent hair color.
Oxidative hair colors rely on two different ingredients that are mixed together just before application: a mixture of alkalizing agent and dye precursor held together by a thickener solution and a hydrogen peroxide solution.
Progressive hair colors--so named because they change the color of hair gradually--rely on lead acetate or bismuth citrate as the active ingredient.
Both types of permanent hair color are irreversible and work by chemically altering hair's biology. Permanent hair color changes hair's pigment by removing some of the hair's protective outer lipid layer, first removing the hair's natural color and then depositing a new color in its place.
The outer layer of the hair shaft is a layer of fatty lipids, sometimes called the F-layer. This layer plays a key role in protecting the hair from heat, water and other potential damaging elements. Hair's outer layer has natural protective powers, including the ability to repel water and self-lubricate. When this layer is removed partially by permanent hair color, so are its protective powers. The change caused by permanent hair color is, by nature, permanent. Long-term, repeated hair coloring can remove hair's protective outer layer completely.
Without its protective outer layer, hair loses its ability to repel water. By absorbing water instead of repelling it, hair becomes more fragile and more likely to sustain damage. Hair that has been dyed with permanent hair color may be more susceptible to tangling. The colored hair may feel dry and rough. Colored hair may also lack shine and look dull.
Some permanent hair color ingredients--those that contain non-approved coal-tar colors--have the potential to penetrate the skin and may pose serious health risks. Animal studies in the 1970s and 1980s found that permanent hair colors containing 4-methoxy-m-phenylenediamine, 4-chloro-m-phenylenediamine, 2,4-toluenediamine, 2-nitro-p-phenylenediamine and 4-amino-2-nitrophenol contributed to cancerous cell formation. Subsequent research, however, questioned the validity of those studies, and in 2006, the U.S. Cosmetic Ingredient Review Panel (CIR) said that based on existing research, there was no clear correlation between use of permanent hair color and cancer risk.
One of the best ways to enjoy the long-term effects of permanent hair color without the problems it can cause is to protect your hair with regular use of conditioner, which can compensate for some of the damage problems that occur when the hair's outer layer is broken by the chemicals in permanent hair color.