Risk of Carcinogenicity Associated with Synthetic Hair Dyeing Formulations: A Biochemical View on Action Mechanisms, Genetic Variation and Prevention

Abstract

Article tries to visualize the potential for carcinogenic trigger in humans with a preference for oxidative synthetic of hair dyeing formulations, especially which belong to the category of permanent colours. According to the International Agency for Cancer, hair dyes for personal use are not strictly classified as carcinogen to humans. However, some controversy exists that requires clarification. Some epidemiological studies support the association between the risk of cancer development and personal use of hair dyes (pooled relative risk RR = 1.50. 95% CI: 1.30–1.98). The world-wide sale of hair dyeing cosmetics have exceeded 15 billion dollars by the year 2012 and has maintained an annual growth rate of 8–10%. This raises concerns and need to be addressed. The review article briefly discusses about the different hair dye components based on their chemical nature, permanence, interaction of dye components with different parts of the hair shaft, action mechanisms, health risk assessment, associated challenges and possible alternatives. There appears variability towards the pathological changes incurred in the human system upon the use of synthetic hair formulations. This probably appears due to the presence of interindividual genetic variation of enzymes handling these xenobiotics. The redox mechanism of major hair dye components appears to be involved in the carcinogenic trigger. Most of the hair dye constituents pose serious health issues. However, we do have few better alternatives to prevent the toxicity associated with hair dye constituents without compromising the need of today’s fashion statement and expectations of the youth.

Introduction

Going back to the era of 1970’s, when hair dyeing was not as common as today, scientists had warned of many harmful effects of the constituents present in hair dyeing formulations. Studies carried out in 1976 clearly pointed out the mutagenicity and carcinogenicity of synthetic hair colourants. According to some of the studies [1–3], the potential carcinogenic effects of over 300 compounds present in hair dyeing products were attributed to their interaction with the information containing macromolecule; deoxyribonucleic acid (DNA). Grey hair has been synonymous with ageing and loss of youth, to hide premature grey hair, youngsters are allured to hair colouring or dyeing. This approach has led to the flourishing of the cosmetic industry with an annual turnover of > 15 billion dollars. Among many cosmetic products like talc, tattoo’s, skin care products and hair dyes, it is the hair dyeing cosmetics which has attracted both the sexes among all the income groups. Though the epidemiological studies have provided evidence of hair dyeing components as potential human carcinogens, still the situation largely remains unresolved due to mixed results. The studies mostly revolve around the risk calculations, establishing correlations and cumulative risk associated with the person developing malignancy. Hair dye users also have a family history of cancers, specifically; bladder cancer, non-Hodgkins and Hodgkins lymphoma, breast and hematological malignancies. There has been a rise in the incidence of bladder cancer (> 50%) with a decline in mortality rates during the past few decades. Since superficial bladder cancer is not fatal and therefore, association with hair dye becomes difficult in such cases unless the study is stratified according to anatomical locations. However, a pooled analysis gave relative risk (RR) equal to 1.50 with 95% confidence interval (CI) (95% CI: 1.30–1.98) [4, 5]. A rise in the incidence was also reported in case of the above mentioned cancers as well. The increase in the incidence of cancers related to hair dye usage is not only due to improved diagnosis but may also be attributed to the type of hair dye in use, duration of application, genetic factors like the ability of enzyme N-acetyl transferase (NAT) to metabolize aromatic amines, smoking and dietary status [6]. The serious public health concern appears to be the causal relationship between cancer development and application of different hair dyes along with the possible redox mechanism of these dye components.

Structure of the hair shaft and its interaction with hair dye components

Hair has a complex morphology. It is made up of mainly three distinct areas that acts as a single unit; the cuticle, the cortex and the medulla. Medulla is usually absent in fine hair and is more visible in coarse hair like that of Asians and Caucasians and also in grey hair. Presence of medulla makes hair more prone to damage and splitting. The cuticle acts as a protective layer around the shaft and is made up of enucleated, flat keratinocytes. Whereas the cortex is an arrangement of vertical bundles of rod-shaped keratin. The exact function of the medulla is not known and it appears as an air-filled space [5].

Depending upon the composition and mechanism of imparting colour, hair dyes are classified as permanent, semi-permanent and temporary (Fig. 1). Permanent hair dyes are colourless and require a developer component hydrogen peroxide (H₂O₂) to produce colour. The more intense the colour the higher is the concentration of harmful chemicals and so more is the expected damage. Oxidative stress starts here and is reflected in the findings of epidemiological studies that darker the colour the more is its potential towards inducing malignancy in human beings. Permanent hair dyes do not just coat the hair, rather they form ionic and covalent bonds and are completely deposited into the cortex. Whereas, on the other side both semi-permanent and temporary hair dyes do not penetrate deeper and they interact with the hair shaft through Vander Walls attractive forces. They produce direct colour and do not require the presence of H₂O₂. The article will focus more on the epidemiological data associated with permanent and semi-permanent hair dyes, their action mechanism, genetic variation of enzymes involved in xenobiotic metabolism and some of the ways to prevent their harmful effects.

Fig. 1.

The figure represents different types of hair dyeing formulations based on their composition and permanence

There is an increase in the sale of hair dyeing products by 8–10% annually around the world. Which is likely to make the population more susceptible to hair dye induced pathological changes. Change is more pronounced in the Asian and Caucasian population due to variation in their genetic makeup and hair structure [7]. Presence of aromatic amines and their derivatives were reported to be carcinogenic in animal subjects [8]. Some of the observational studies have reported about increasing cases of malignancy among hair dressers [9]. However meta-analysis of epidemiological studies failed to provide any strong association with the rising incidence of cancer among hair dressers [10, 11]. These areas of conflict need to be clarified before establishing any causal effect. Whatever the case may be, most of the studies do support a higher risk of cancer development in Asians using black permanent formulations than Caucasians, due to their genetic makeup and choice of colour [12].

Challenges in Linking Personal Use of Hair Dye and the Risk of Cancer Development

Most of the analytical epidemiological studies on human subjects take advantage of biomarkers to establish the link between exogenous carcinogens and the risk of cancer development. Biomarkers act as a connection to access causality and as a molecular signature of chemical exposure [13]. The difficulty is that the laboratory studies (using animal models) and the studies on human population need to formulate a specie specific mechanism of action of these compounds along with stratification of the data at the level of duration of exposure, age, sex and route of exposure [14, 15]. Another challenge is the lack of regulatory power of the Food, Drug and Cosmetic Act (FDCA-1938) and its limitation only to pre market testing of the cosmetic product. Therefore, it lacks the power to assess the chemicals before they are included as product component. This puts the consumer at risk, as it also does not require the manufacturing companies to report about the safety of any other component that has been included in the product. It only allows FDA to label the product as adulterated [16, 17]. By the law if there is any adverse event reporting, manufacturers are not required to forward it to FDA. A case could be quoted where a hair dyeing company received > 2100 adverse events reported directly from its consumers. However, out of 2100 only 127 reports were forwarded to FDA [17]. The data obtained through Centre for Food Safety and Applied Nutrition’s Adverse Event Reporting System (CAERS) does not require information about patient’s demography and cancer subtyping. The reported data obtained would be of more statistical significance if it included; family history, associated comorbid conditions and behavioural characteristics [18–20]. Despite these facts the better side of the situation is that the Food and Drug Administration (United States) has made the CAERS more transparent in 2016. The data is now publicly available. Also, adverse event reporting is being encouraged from the consumer side. Along with other cosmetic products, hair dyes and other hair products are included for adverse event reporting.

Possible Biochemical and Molecular Mechanisms for Triggering Malignant Events Upon the Use of Hair Dyes

There appears to be a rising trend of hair dye use all over the world. More than 1/3rd of an estimated population of the United States above 18 years of age use hair dyeing formulations [21]. Preference for these formulations is usually of permanent nature. Most of them contain 3000–5000 potential chemicals, that have been reported to be mutagenic as well as carcinogenic in nature (Table 1). The property of these chemicals to induce malignant changes could be because of these proposed mechanisms [22, 23], (a) they act as an endocrine disrupting agent, (b) Phenylenediamine induced inhibition of cell signalling, (c) Photo cytotoxic effect of dye components, (d) Formation of direct DNA adducts. Hair dyes (mostly permanent) contain derivatives of aromatic amines [21] like para phenylenediamine (PPD), 4-chloro-orthohenylenediamine (4-cl-OPD), 2,4-diaminoanisole sulphate and 4-aminobiphenyl (ABP). These compounds are readily absorbed in the blood stream, they can interact with the macromolecule like DNA and proteins to form adducts [24, 25]. They are also reported to alter the structure and conformation of these macromolecules. Some of the compounds like ABP are shown to play critical role in the development of breast cancer. Aromatic amines can enter the circulation, reach breast ductal epithelial cells and form ABP-DNA adducts in the breast tissue [26, 27]. Studies following long term exposure of hair dyes (> 5 years, twice a month) reported, statistically significant association, between permanent dark coloured hair dyes and ER + breast cancer. Also, the study showed no association with ER- cases [28]. Most of the data available, support the association but happens to present weak evidence, hence this is the area that needs to be explored to find out the mechanism where hormones interplay along with the dye components [29–32]. An active ingredient of permanent hair dyes; PPD is reported to interfere and inhibit cell signalling pathways known to regulate cell proliferation and cell differentiation. PPD acts through the production of reactive oxygen species (ROS). Generation of oxidative stress leads to inhibition of Wnt, mToR and NF-κB pathways in the mitochondria. The overall effect is the accumulation of lipid peroxidation products and unregulated cell apoptosis. If this progresses and goes unchecked, it may lead to the disruption of mitochondrial membrane potential and the release of cytochrome c [33]. This could be one of the reasons for the hair dye formulation containing PPD to show a positive association with carcinogenicity. A recent study reported an increased risk for the development of lymphocytic leukaemia with the use of permanent hair dyes. Lymphocytes are quite susceptible to PPD. Lymphocytes exposed to PPD showed the presence of DNA strand breaks [34–36]. Photo-oxidation of some hair dyeing compounds release photo products, formed upon exposure to UVA/B rays. This further enhances oxidative stress induced cytotoxicity. PPD and its derivatives can be detected 48 h post- application of dark coloured (brown and black) permanent hair dye [37]. Upon application, the aromatic amines are absorbed by the skin, compounds being photosensitive, when exposed to sunlight they get activated. Photo sensitized cosmetic hair dye components induce oxidative stress through the release of O₂⁻ and^.OH radicals (Fig. 2). All the reactive oxygen species generated with in the cell, trigger a sequence of events that include DNA single and double-strand breaks, formation of pyrimidine dimers, lipid peroxidation products and protein aggregates. These progressive changes may become the basis of carcinogenicity and other pathological inflammatory responses. This appears to be a matter of concern for persons residing in countries with tropical weather [38, 39]. Few of the permanent and most of the semi-permanent hair dyes still contain azo derived pigments. The most common being Basic Red 51 (BR 51) and Basic Brown 17 (BB17). These are the main components of semi-permanent hair dyes. Azo compounds (R = N = N–R′) are readily absorbed by the skin and enter circulation. Benzidine based azo dyes undergo N-Acetylation to form reactive DNA binding compounds that can initiate a sequence of pathological events, like the release of pro- inflammatory cytokines, breakdown of tolerance, mutagenicity and triggering carcinogenic events. Most of these compounds show toxic effect at concentrations much less than that present in commercially available formulations in the market.

Table 1.

Important documented changes in the composition of hair dye formulations

Hair dye component	Year of change	Potential effect	References
2,4-diamino anisole	Removed between 1970 and 1980	Carcinogenic and mutagenic in animal subjects. Forms adduct with DNA and proteins. Induces oxidative stress	[40]
2-nitro para phenylenediamine	Used till late 1990	Form adducts with DNA and proteins. Induce oxidative stress	[40]
4-amino biphenyl	Prohibited by European Union in 2004 Regulated in the United States Still in use in many countries	Positive association with bladder cancer No association with lymphoma	[7, 41]
Azo dyes	Some removed in 1970 and early 1980 Some still in use as a component of semipermanent hair dye	Positive association with bladder cancer and lymphoma	[40, 42, 43]

Fig. 2.

The figure represents the deleterious effects of synthetic hair dye formulations

Genetic Variation in Genes Involved in DNA Repair Modifies Susceptibility Towards Hair Dye Associated Cancers

Hair dyes usually contain aromatic amines and their derivatives. PPD and ABP appear to be the most common one. The human system handles these exogenous components through biotransformation of xenobiotics which involves different metabolizing enzymes to make the component more soluble. Mostly the procedure is operative in hepatic tissues and a part of it in extra hepatic tissue as well. The sensitivity of these toxic chemicals varies due to the presence of different isozymes or isoforms of the enzymes, which are involved in the process of detoxification. One of the steps is through acetylation. The enzymes involved in the process of biotransformation of these aromatic amines include mainly N-acetyl transferases (NAT) and glutathione S-transferase (GST). Both the enzymes are the products of two polymorphic genes forms i.e., NAT1, NAT2, GSTM1 and GSTT1. They differ in their degree of acetylation and transformation of xenobiotic compounds. Humans show inter individual genetic variations in NAT and GSH genes. Therefore, the level and activity of their protein products are also variable [44, 45]. These variations appear to be responsible for the differences in pathological susceptibility towards different toxins. The isoforms of NAT (NAT1 and 2) show 81% amino acid sequence homology, still their affinity and kinetic sensitivity towards aromatic amines is quite different [46]. This would result in variable acetylation capability [47]. There is a chance that some people may be more susceptible to the effect of the mentioned hair dye components than the others. The distribution of NAT isoform is tissue specific. NAT 1 is present in almost all the tissues including skin, where the dye component first encounters the enzyme [48, 49] Whereas NAT 2 is expressed predominantly in the liver [49]. Both NAT 1 and NAT 2 are involved in the acetylation of aromatic amines, hence they both are involved in the process of detoxification. A case-controlled study carried out in America involving 1321 cases and 1057 controls, assessed the risk associated with non-Hodgkins lymphoma and permanent dark coloured hair dye use. The study by Morton et al. reported an increased risk of non-Hodgkins lymphoma in women using dark permanent hair dye before 1980’s, they also reported that the risk increased with NAT 2 rapid acetylation phenotype but not with slow phenotype [40]. Another study stratified for NAT 1 and NAT 2 however showed no association between hair dye use and risk of bladder cancer [50]. It is known that only xenobiotics that are not bound to carrier proteins can become the part of glomerular filtrate. They may get reabsorbed through tubular cells and so their deposition inside the bladder depends on total urinary excretion that takes into account both glomerular filtration and secretion across tubule cells. A large case–control study identified an association between the risk of bladder cancer development with hair dye use and NAT 2 phenotype. They also reported that NAT1, GSTM1 and GSTT1 failed to establish a significant association with the risk of developing bladder cancer with permanent use of hair dye [51]. Though many studies report the association of permanent hair dyes with bladder cancer [52–54], still, some do not. Important to note here, is that, genetic polymorphism does appear to influence aromatic amine biotransformation related bladder cancer risk [51, 55] and the risk associated with non-Hodgkin’s lymphoma [6].

Hair Dye Use and Risk of Human Cancer

The scientific community has been in a quest to identify the potential risk associated between hair dye use and human cancer. Many epidemiological studies have been carried out to identify and understand this relationship (Table 2). However, the relationship was found to vary according to the type and subtype of cancer, frequency and type of hair dye formulation used. A systematic literature review on the association between personal use of hair dye and risk of leukaemia reported a meta-relative risk of 1.09 at 95% confidence interval (CI: 0.97–1.22). The result is reported to be pooled from 20 studies and the controls were non-hair dye users. They also reported that when the analysis was adjusted for smoking, the meta-relative risk was found to be 0.99 at 95% confidence interval (CI: 0.76–1.29) [36]. Another study reported a 15% higher risk of developing hematopoietic cancer among people using hair dye compared to non-users [10]. Studies also provided evidence that smoking, type of hair dye, duration of use and gender may be few factors directly associated with the risk of leukaemia [34, 36, 56, 57]. Smoking is a risk factor for the development of acute and chronic myeloid leukaemia. Cigarette smoke contains benzene and its derivatives, which are known potential carcinogens. Epidemiological studies adjusted for smoking presented a reduced risk for developing leukaemia. This is suggestive of high prevalence of smoking among hair dye users than non-users [58]. Research also supports that the type of hair dye i.e., permanent dark pigmented colour use is associated with a greater risk of developing leukaemia than semi-permanent or temporary hair dyes [59, 60]. Since many of the studies did not adjust for smoking, hence, may face bias. Still, over-all the finding of most of the studies support the use of hair dye to be associated as the risk factor for leukaemia.

Table 2.

Summary of some recent literature on the association between personal use of hair dye and risk of cancer development

Type of the study#	No of cases included	Odds Ratio (OR)	Type of hair dye studied	References
Case–control study (population based)	2982 cases and 5782 controls	OR = 1.4, 95% CI:1.0–1.9	Black permanent	[39]
Case–control study (Bladder cancer)	897 cases and 897 controls	3.3-fold increase 95% CI: 1.3–8.4	Permanent	[61]
Case–control study (Breast cancer)	884 cases and 960 controls	Relative risk (RR) = 1.3, 95% CI: 1.0–1.6	Permanent and semipermanent	[62]
Case–control study (Breast cancer)	608 cases and 609 controls	No risk association was reported	Combination of hair dyeing products	[30]
Case–control study (non-Hodgkin’s lymphoma)	1321 cases and 1,057 controls	OR = 3.3, 95% CI: 1.3–8.6	Permanent hair dye use with NAT 2 phenotype	[40]
Case–control study (hematolymphopoietic malignancies)*	1183 cases and 828 controls	OR = 2.0, 95% CI:1.1–3.8	Permanent dark coloured	[63]
Case–control study (Myelodysplastic cancer)	111 cases and 830 controls	OR = 1.99, 95% CI: 1.77–3.38	No specific type	[64]
Hospital-based case control study (childhood brain tumour)	540 cases (biological mothers) and 801 matched controls	OR = 1.9, 95% CI: 0.5–7.0	Hair dye with nitroso compounds	[65]
Hospital-based case control study (neuroblastoma)	538 cases and 504 control	OR = 1.6, 95% CI: 1.2–2.2	Any hair dye	[66]

^#In most of the cases, cohort studies failed to establish any risk associated with hair dye use and human cancer

*Most of the case–control studies suggest no association between risk of leukaemia and use of hair dyes [67–69] and some even suggested an inverse relationship [70, 71]

Findings involving the association between hair dye use and breast cancer have not been so clear, rather they are inconsistent. Most of the studies reported no risk association between hair dye use and breast cancer [72–74]. While on the other hand few of the studies do report a positive association [75–78]. A prospective cohort study carried out in the United States from 2003 to 2009 involving 50,884 women aged 35–74 years with no history of breast cancer using personal hair dye reported the hazard ratio (HR) equal to 1.09 at 95% confidence interval (95% CI: 1.01–1.17). They reported that the association of breast cancer vary with race (black women using permanent hair dye had 45% more chance of developing breast cancer), frequency of use (increased frequency was positively associated with the risk of breast cancer). Black women who used dye every 5–8 weeks were reported to have a 60% higher risk for developing breast cancer. The study also mentioned that use of semi-permanent or temporary hair dye was not associated with the risk of breast cancer development [79]. A case–control study was conducted in New York City on African American (AA) and White American (WA) women. The study included 1,508 AA and 772 WA with histologically confirmed invasive breast cancer cases and 1,290 AA and 715 WA as controls, reported 51% increase (Odds ratio = 1.51. 95% CI: 1.20–1.90) in overall risk of breast cancer on personal use of dark coloured hair dye products. They also reported a 72% increase in breast cancer risk with dark shades and a 36% increase in ER + disease risk with an increase in the frequency of use [80]. Population studies were also carried out to establish an association for bladder cancer, non-Hodgkins lymphoma, Hodgkins lymphoma and multiple myeloma. Few studies are there on cancers like salivary gland [81], brain [82], Kidney, lung and ovary [83]. Most of the case–control studies on bladder cancer either reported a low-risk association between bladder cancer and hair dye use or the study sample was too small to establish a significant relationship [50, 84]. Whereas cohort studies in general report no association between bladder cancer and personal use of hair dye [42, 67]. In the case of non-Hodgkins and Hodgkins lymphoma, both case–control and cohort studies were in favour that hair dye use does not involve the risk associated for development of non-Hodgkins and Hodgkins lymphoma [39]. Results of most of the case control studies for multiple myeloma were inconsistent, some however reported an increased risk association with hair dye use [85, 86], while others found no association [42, 44, 67]. The results of cohort studies could not find any significant association between the use of hair dye and risk of multiple myeloma [67, 87].

Factors that Could Minimize the Risk Associated with Hair Dye Usage and Cancer

A hospital-based case control study conducted in Taiwan between August 2000 and December 2008 involving histologically confirmed 296 prostate cancer cases and 296 age matched controls, reported 15% increase in the risk of prostate cancer with the use of hair dye (once every three months for at least 1 year) compared to non-users (OR = 2.15, 95% CI = 1.32–3.57). They reported no risk association with cancer survival compared to non-users. The study also reported that regular exercise could reduce the risk associated with prostate cancer related death. However, exercise could not prevent the risk of developing prostate cancer [88]. Studies are also there that favour and suggest recreational physical activity to protect from the adverse outcomes of prostate cancer, but again there are studies that report no association between recreational activity and the risk of prostate cancer development [89]. Some studies do suggest the positive effect of physical activity on cancer patients, in general the improved survival rate of prostate cancer patients could be due to improved antioxidant and immune activity of the exercising person. Moreover, exercise regulates the release of growth factors and hormones like androgens and insulin that could up to some extent control the aggressiveness of such cancers [90].

Besides exercise, some other ways to prevent the risk associated with the use of synthetic formulation are: (a) introduce natural plant derived pigments into synthetic formulations, (b) use of synthetic eco-friendly hair dyeing formulations and (c) use of naturally available hair colourants (Fig. 3). Most of the people going for hair dyeing are now aware about the risk associated with synthetic formulations having aromatic amines or even azo compounds. A new study suggested addition of plant derived hair dyes to synthetic formulations [91]. The natural components being safe and non-toxic could reduce the harmful effects of chemical constituents of synthetic formulations. Introduction of fungal Laccase to produce plant polymerized colourant is a new emerging colour imparting technique. The technique is encouraged as it can be used as an alternative to the available synthetic dyes in the market [92]. The only thing is that the hair dyeing process would take a longer time as compared to recently available commercial products. The good thing is that this formulation has shown resistance towards detergent treatments [91, 92]. Still, what the best option appears is to adopt natural colouring methods like the extracts of Lawsonia inermis [93], anthocyanin from Zea mays [94] and Camelia sinensis [95].

Fig. 3.

Action mechanism of natural hair dye component 1,4-napthoquinone and 2-hydroxy-1,4- napthoquinone. Ahr; represents aryl hydrocarbon receptor. Napthoquinone forms complex with Ahr to mediate anti-inflammatory responses and improves healing of late epidermis. The addition of Para phenylenediamine (PPD) to natural hair colourants forms stable but toxic formulation

Conclusion

Epidemiological studies on human cancer do support the association between hair dye use and the risk of some specific cancers. However, there is limited evidence in this direction. The studies also establish the role of polymorphic genes involved in the biotransformation of aromatic amines. The presence of polymorphic genes could modify the risk associated with personal use of hair dye and human cancer. There is an increasing demand of hair colouring products and is well accepted among the youth. This raises concerns and requires a deeper understanding of its constituents. Most of the hair dye constituents enter the circulation and pose serious health issues, either through photo-oxidation or direct free radical mechanism, therefore, flexibility to adopt some safe alterations should be a priority.

Author Contributions

Idea and conceptualization: AA, Critical revision and editing: M, Conceptualization: SA, Final revision and editing: SF and SAA, Idea, literature search and drafting: SH. All the authors have read and approved the final manuscript.

Funding

No funding was received to assist with the preparation of this manuscript.

Declarations

Conflict of interest

The authors have no relevant financial or non-financial interests to disclose.