 Hair dyeing has been practiced for centuries, but the development of dyes in the last century or so have included chemicals that may be carcinogenic, that may cause cancer. Watch to see what the science says about the risk. Since there's typically no way to reverse hair color loss, the use of hair colorants is a mainstay of management. A practice documented as far back as 1500 BCE. While gray hair may carry a distinguished look and limit women's subjection to a sexualized gaze, hair color constitutes a multi-billion dollar market, with up to 60% of men and women in Western countries choosing to use coloring products, many of which to cover gray. For over a century, aromatic amines have been the main chemicals used in commercial permanent oxidative hair dyes. The primary problem with these compounds is that they can be potent contact allergens. Product labels often recommend a small 48-hour test application to the skin before use, but it can take up to a week for a skin allergy to flare up. They also may cause cancer. Hair products contain more than 5,000 chemicals, and so it's hard to narrow it down. But the aromatic amines, such as paraffiniline dye mean, that are often used in hair dyes to prevent fading due to washing, have been picked out as a probable carcinogen. Before industry reformulation in response to mandated cancer warning labels, 9 out of 10 permanent hair dye products were mutagenic, meaning capable of causing DNA mutations. This then appeared to translate into more than 10 times the odds of DNA damage in breast cells obtained from the breast milk of women who had used hair dye in the last six months compared to not using hair dyes at all. But does that translate into more cancer? A meta-analysis of 42 studies found that hairdressers, particularly those who held their jobs 10 or more years, were at significantly higher risk of developing bladder cancer later in life. Hairdressers, beauticians, and barbers may also suffer more lung cancer, voice box cancer, and multiple myeloma. There is some evidence that hairdressers may smoke more, but the researchers took this into account. They conclude that salon should be better ventilated, that gloves should be used, but how much is that going to help the person whose head has been soaked in it? Based on testing for radioactively traced hair dye ingredients in the urine, experiments suggest exposure to hair dye may be several hundred fold higher in hair dye users than the occupational risk to the hairdressers. But thankfully, there does not seem to be an excess risk of bladder cancer among those who just use hair dye personally. Furthermore, major changes took place in the 1980s to make hair dyes safer. In 1979, the U.S. Food and Drug Administration started requiring cancer warning labels on hair dye products leading the industry to start reformulating to eliminate the most carcinogenic ingredients. A turning point in bladder cancer risk isn't apparent from the data, but this may be a function of the long latency time between exposure and malignancy for bladder cancer, which can be 30 or 40 years. If you look at faster developing cancers such as leukemia or follicular lymphoma, there does seem to be a drop-off in risk after 1980, though a 2019 meta-announce is looking at increased non-Hodgkin's lymphoma risk without consideration of date range concluded exposure to hair colorants should be reduced as much as possible. For prostate cancer, the doubling of odds associated with hair dye use seems limited to pre-1980 exposure, and there appears to be no link to brain tumors in either time frame. As a tragically ironic aside, while the risk associated with hair products may have declined for white men and women, the opposite trend seems to have occurred for certain hair products targeted towards African Americans. The Black Women's Health Study, which assessed the exposure in the 1990s, found no association between breast cancer and the use of hair relaxers, chemical treatments used to straighten hair. But in the early 2000s, popular straighteners switched from non-carcinogenic compounds like lye to chemical cocktails containing formaldehyde. So now, frequent straighteners use is associated with about a 30% higher breast cancer risk. Thankfully, there's been a shift towards embracing more natural hairstyles in the African American community, resulting in the sales of hair relaxers falling by 40% in recent years.