Dyeing hair has been a long-standing cosmetic practice of changing the color of one’s hair to a more desirable color. In ancient times, hair coloring was often achieved through the use of plant-derived dyes. Some examples of these include: indigo, henna, and amla. Today, however, hair dyeing is often completed by a mixture of both natural plant-derived dyes and synthetic dyes. Synthetic dyes are chemically synthesized organic compounds made from chemical reactions. A common synthetic component of modern hair dyes is p-Phenylenediamine (PPD), which is a type of coal tar dye derived from petroleum. PPD, in combination, with hydrogen peroxide and ammonia, are the basic ingredients in modern hair dyes.

How Do Hair Dyes Work?

The first step to dyeing hair is to remove any color from the hair. This is a process known as bleaching. The main compounds used in this step are hydrogen peroxide and ammonia. Ammonia is used to separate the hair proteins, so that the dye can reach the hair shaft for a long-lasting look. Hydrogen peroxide is an oxidizing agent that bleaches the hair, as the oxidizing reaction removes color from the hair. At the same time, hydrogen peroxide can also oxidize the proteins found in hair, leading to the hair feeling brittle as its protein structure has been damaged. 

Once the hair has been bleached, the coloring agents of the hair, known as intermediates, can then be added. PPD is the most basic of these intermediates and is commonly used as a starting block. When PPD reacts with the hydrogen peroxide already on the hair, it produces dye molecules, which is what colors the hair. PPD alone with hydrogen peroxide leads to a brown color; to make other colors, other compounds, called coupling agents, are added to the mix. These coupling agents interact with PPD and hydrogen peroxide, thus leading to unique colors based on the combination of coupling agents added to PPD and hydrogen peroxide. 

What are the Possible Dangers of Hair Dyes?

There are considerable risks that are associated with many of the compounds used in modern hair dyes. A major example would be PPD. PPD, due to its coal-tar nature, has been known to be a carcinogen, in addition to being a common allergen. PPD has also been associated with blood toxicity and birth defects.

Other molecules, such as ammonia and hydrogen peroxide, are irritants, especially when breathed in. Lead acetate, another common ingredient of hair dyes, is a neurotoxin. 

However, the most dangerous part of hair dyes is the fact that they are unregulated by the FDA. This means that potentially dangerous compounds, like PPD, are still commonly used in hair dyes sold in the U.S., along with many other lesser known compounds. 

The Bottom Line

Hair dyeing is something that should be done occasionally and properly, as that is the best way to lower the risk of adverse effects. In addition, reading the ingredients label on hair dyes and doing your own research on these ingredients is the safest way to know what is being put into your hair and to be prepared for any possible side effects.