117 Chapter 4 Hair Coloring Jennifer M. Marsh, The Procter & Gamble Company Introduction The natural color of human hair has a profound influence on appearance and reflects both age and ethnic origin. However, for thousands of years products have been applied to hair to change its color. Ancient Egyptians used plant and animal products such as berries, tree bark and insects to darken hair, as well as the leaves of the henna plant (Lawsonia inermis) to impart a red tint, a practice still in use today. During the Renaissance, techniques were discovered to lighten natural hair color using potassium lye or caustic soda in combination with strong sunlight. In 1867 a milder way to lighten hair was identified, using hydrogen peroxide, an oxidizing agent first isolated in 1818 by Louis Jacques Thénard. During this time the first synthetic organic dyes were being discovered that could give a wide range of natural shades. The amino dye p-phenylene diamine was patented for hair dyeing in 1888 by E. Erdmann, and by 1906 the first commercial product based on these dyes and using hydrogen peroxide as a pre-lightener was being used in salons by L’Oreal. It wasn’t until the 1950s that Clairol produced a one-step product to allow consumers to color at home using essentially the same chemistry. Today the majority of hair colorant products use the same oxidative dyes to form color and hydrogen peroxide to lighten hair but the range of products