Hair is an indicator of attractiveness, femininity, masculinity, health, and beauty. As society focuses more and more on youthfulness and beauty, hair dyeing has become popular among both men and women pursuing such value or fashion trends. Globally, hair colorants are a rapidly growing industry of over $7 billion (The Economist, 2015). Hair dyeing involves treatment of the hair with various natural and/or artificial chemical compounds mainly for cosmetic purposes (e.g., to cover gray hair, to change to a color regarded as more fashionable or desirable at a given time, etc.).
The association between hair dye application and the development of cancer has been a topic of debate over the past several decades. Hair dyes come in two forms: (i) oxidative (permanent) and (ii) non-oxidative (semi-permanent and temporary) (USFDA, 2014). Permanent dyes consist of primary intermediates (e.g., p-phenylenediamines (PPDs) and p-aminophenols) and couplers (e.g., m-aminophenols and m-hydroxyphenols) in the presence of peroxide (USFDA, 2014). Non-oxidative hair dyes include colored compounds that stain hair directly. Some of the chemicals used in hair dye products are reported to be carcinogenic in animals (Bolt and Golka, 2007). Likewise, the International Agency for Research on Cancer (IARC) reported that some of the chemicals in hair dye are probably carcinogenic to those who are exposed to them occupationally (e.g., hairdressers and barbers). However, hair dye products have not yet been classified as carcinogenic for personal users (IARC, 2010).
Given the widespread use of hair dye products around the globe, scientists have tried to determine the association between hair coloring products with health risk. In this review article, we provide a critical assessment of this issue by exploring the impact of hair dye on human health. This effort will help to gain better knowledge regarding contradictory or controversial myths about the use of hair dye and its possible cancer risk. To this end, the available data for meta-analytic studies for bladder, hematological, breast, skin, ovarian, and cervical malignancies have been evaluated on a parallel basis. Based on this review, we aim to provide up-to-date knowledge on the use of hair dye products and their possible impact on human health.