Hair coloring is not a new practice; people have been changing their hair color since the era before Christ (1). The Romans had a preference to dark hair, and to fulfill this desire, they used boiled walnuts together with leeks to create the dye. They also used henna, sage and indigo plants to darken their hair (2). Ancient Greeks believed that blonde hair represented honor and courage and that is why men dyed their hair with harsh soaps and bleaches (3). During the Renaissance, blonde hair was considered appealing, so women would mix black sulphur, alum and honey to lighten their hair in the sun (2). In 1907, French chemist Eugene Schueller discovered the first synthetic hair dye with a new chemical called paraphenylenediamine. After his discovery, he founded the French Harmless Hair Dye Company, which the name then became L’Oreal (4).
General Features of Hair
Human hair is a tissue that contains keratins that are insoluble proteins composed of eight amino acids (5), which grows from the bulb of follicles stretching from the surface of the skin through the epidermis, and lastly to the dermis. The growth cycle of hair is controlled by the dermal papilla, located at the center of the bulb. Basal layers produce hair cells, and surround the bulb. The hair pigment is produced by melanocytes that are inside the bulb. Blood vessels close to the base of the bulb maintain the growth of hair. The growth of hair is a cycle with three stages t called, anagen, catagen, and telogen. During the first stage the hair fiber grows for two to six years. At the catagen stage, growth of the hair fiber slows down at the dermal papilla. The bulb shrinks and goes towards the epidermal surface and last for two to three weeks. At the last stage the growth stops, and a new bulb originates from under the shrunken bulb, where it eliminates the old hair fiber and produces a new one. It lasts for six to twelve weeks. Hair grows at more or less...