This latest research involved more than 5000 people in the UK with and without primary biliary cirrhosis (PBC), an early stage of liver cirrhosis. Using detailed postal questionnaires, the study found that around 1 per cent of men, and more than 50 per cent of women, used hair dye, and that this was associated with a 37-per-cent increased risk of PBC.
Smoking was also linked to the disease but, surprisingly, drinking was not (Gut, 2010; 59: 508-12).
Although the findings aren't proof that hair dye causes PBC, the authors suspect that octynoic acid-a chemical found in hair dye, nail polish and other cosmetics-could be responsible for the connection. Indeed, there's convincing evidence from both animal and test-tube studies to substantiate such an hypothesis (J Autoimmun, 2006; 27: 7-16; J Immunol, 2005; 174: 5874-83). In humans, there's also a study linking PBC with frequent use of nail polish (Hepatology, 2005; 42: 1194-202).
Other hair-dye chemicals-including toluidine and p-aminophenol-are also plausible causes of liver damage (Chin Med J [Engl], 2009; 122: 875-7). In a Japanese study of 15 factory workers who handled toluidine from three to 20 times, seven showed signs of liver damage, and three were hospitalized because of acute liver dysfunction (Gut, 2002; 50: 266-70). p-Aminophenol has been shown to cause liver damage in mice (J Biochem Mol Toxicol, 2001; 15: 34-40).
While more studies are needed, there's already considerable evidence to suggest that using hair dye on a regular basis could be contributing to liver disease, especially in women.
If that's not enough to put you off colouring your hair, there's also evidence linking hair-dye use to cancer, including rare cancers such as non-Hodgkin's lymphoma (NHL).
A possible connection was first noted in the 1970s, when several studies found links between hair dyes-particularly the black, dark-brown and red shades-and breast cancer (NY State J Med, 1976; 76: 394-6; J Natl Cancer Inst, 1979; 62: 277-83). What's more, women who had started dyeing their hair in their 20s had twice the risk of the 40-year-olds. However, the users who were at greatest risk were those aged 50-79 years who had been dyeing their hair for years. Moreover, compared with women who had never coloured their hair, those who dyed their hair five or more times a year had twice the risk of developing ovarian cancer (Int J Cancer, 1993; 55: 408-10).
It was also discovered that people who had worked for 10 or more years as hairdressers or barbers had a fivefold greater risk of bladder cancer than the general population (Int J Cancer, 2001; 91: 575-9). More recently, a meta-analysis, which pooled the results of 247 studies, similarly concluded that hairdressers have a greater overall risk of cancer-in particular, lung, larynx and bladder cancers, and multiple myeloma-than the rest of the population (Int J Epidemiol, 2009; 38: 1512-31).
However, it's the link with otherwise unusual cancers that provides the most compelling evidence of hair-dye toxicity. Dyeing your hair can increase the risk of NHL and multiple myeloma from two to four times over a non-user's risk (Am J Public Health, 1988; 78: 570-1; J Natl Cancer Inst, 1994; 86: 210-5). Indeed, hair dyes may account for as much as 20 per cent of all cases of NHL in women (Cancer Res, 1992; 52 [19 Suppl]: 496s-500s).
Nevertheless, there are studies that dispute the cancer connection with hair dyes. Indeed, as a 1993 report by the International Agency for Research on Cancer (IARC) concluded, "There is inadequate evidence that personal use of hair colorants entails exposures that are carcinogenic". However, the report also stated that being a hairdresser or barber entails exposures that are "probably carcinogenic", suggesting that hair dyes may well lead to cancer.
The problem may lie with the older hair-dye formulations, which were considerably more toxic than the newer compounds used these days. One study found an increased risk for NHL in women who used hair dye-particularly the darker, permanent types-before 1980, but no risk for those who began colouring their hair after that time (Am J Epidemiol, 2004; 159: 148-54).
However, the researchers admit that this finding may also be because "recent users are still in their induction and latent periods". Indeed, chemically induced cancers typically take more than 20 years to develop (Crit Rev Toxicol, 2007; 37: 521-36). So, it may not be that the new dyes don't cause cancer, but just that it's too soon to tell.
Another factor that might explain the inconsistent findings is genes. Genomics-the new branch of genetics that studies gene mapping and DNA sequencing-has revealed that some individuals have variations (known as 'polymorphisms') within genes that encode for certain detoxification enzymes. This means that they have greater difficulty clearing environmental toxins from the body (see WDDTY vol 20 no 10), and might also explain why some people may be at greater risk of cancer from using hair dye.
In fact, two recent studies of hair-dye use have found an increased risk of NHL only among women with specific genetic polymorphisms (Am J Epidemiol, 2009; 170: 1222-30; Carcino-genesis, 2007; 28: 1759-64). It's possible, therefore, that a genetic inability to adequately remove toxic hair-dye chemicals from the body could lead to cancer.
Happily, a number of ingredients commonly used in hair dye are now under restricted use and-at least in Europe-some agents have even been banned completely. However, the current formulations may still be hazardous to health.
One chemical of concern is a component of permanent hair dyes called para-phenylenediamine, or PPD. It's still found in more than two-thirds of hair dyes on the market, including many of the top-selling brands. PPD is an effective colorant because its low molecular weight enhances its ability to penetrate the hair shaft and follicle, and it also has a strong protein-binding capacity. However, these properties also make PPD an ideal contact allergen-and, in fact, it's among the most potent of such allergens around.
Over the past few decades, allergic reactions to PPD have become such a serious problem that the chemical has been banned completely from hair dyes in Germany, France and Sweden. Nevertheless, the current European legislation allows PPD to comprise up to 6 per cent of the constituents of personal-use hair dyes.
In addition, despite its restricted use, dermatologists continue to report increasing numbers of cases of PPD-induced contact dermatitis.
A 2007 survey of adults in a London clinic found that cases have doubled since 2001, and it's likely that the increased personal use of hair dye is to blame. The same clinic confirmed that, during the 1965-1975 decade, it saw up to 11 patients a year with non-occupational (they weren't hairdressers) PPD allergy whereas, recently, that figure has grown to more than 40 cases annually. Indeed, it's a trend that has also been observed in other countries (BMJ, 2007; 334: 220).
A patient with contact allergy to hair dye often presents with a simple rash on the face or around the hairline. But severe reactions may also occur. One consumer complaint-based study in Denmark identified 55 cases of severe acute contact dermatitis caused by hair dye, with gross swelling of the face, scalp and ears. These cases were responsible for 75 visits to the health service and five admissions to hospital, leading the researchers to conclude that PPD, at its current concentrations in hair dye, "presents a significant health risk for the population" (Contact Dermatitis, 2002; 47: 299-303). Severe hair-dye reactions among children have also been reported (Contact Dermatitis, 2006; 54: 87-91).
Even hair dyes containing relatively small concentrations of PPD can be a problem, as the chemical accumulates in skin over time. This means that intermittent exposure to lower levels of PPD, such as from regular hair-colouring, could elicit the same reaction as a one-off exposure to a higher concentration (Contact Dermatitis, 2007; 56: 262-5).
Another problem with PPD is cross-sensitization. This means that once you have reacted to PPD, you may become sensitive to its chemical cousins. These are commonly used in other sorts of hair dyes, textile dyes, pen ink, food dyes, medication dyes, preservatives (parabens) and some drugs (such as benzocaine, procaine and sulphonamides). So, an allergy to PPD can be a long-term problem (Frosch PJ et al., eds. Contact Dermatitis, 4th edn. Heidelberg, Germany: Springer-Verlag, 2006: 479).
Sensitization to PPD has also been seen in connection with its use as black 'henna' skin paint for temp-orary tattoos (J Cosmet Dermatol, 2003;
2: 126-30). Interestingly, PPD is not permitted for this type of use. As the US Food and Drug Administration (FDA) states, it is not approved for direct application to the skin (www.cfsan.fda.gov/~dms/cos-tatt.html). Be that as it may, when hair dye is applied, it inevitably comes into direct contact with the scalp and skin on the forehead and around the ears. So, the fact that it triggers allergic reactions in some people is hardly surprising.
In addition to PPD, a host of other potentially dangerous chemicals-many of which rapidly penetrate the skin-can be found in the hair-dye products currently on the market. It appears that octynoic acid may well be a cause of the progressive liver disease primary biliary cirrhosis, and 4-aminophenol (an alternative name for p-aminophenol), another current hair-colouring ingredient, is "a recognized human urinary bladder carcinogen" (Chem Res Toxicol, 2003; 16: 1162-73).
This means that, so far, we can only guess at what effects the combination of chemicals used in hair dyes will ultimately have on our health.
Fortunately, an entire industry has now emerged that is devoted to hair-colouring alternatives. However, many so-called natural products may still contain as many toxic agents as conventional brands, which means that it's up to the consumer to be vigilant and to choose the safest products available (see box, page 19). Alternatively, perhaps it's time to embrace your natural look or to consider growing grey gracefully.
WDDTY VOL 21 NO 2