International Agency for Research on Cancer (IARC) - Summaries & Evaluations

Occupation as a hairdresser (Group 2A)
Personal use of hair colourants (Group 3)

For definition of Groups, see Preamble Evaluation.

VOL.: 57 (1993) (p. 43)

5. Summary of Data Reported and Evaluation

5.1 Exposure data

Since the early twentieth century, hairdressers have made use of a wide range of products, including hair colourants and bleaches, shampoos and conditioners, hair styling preparations and nail and skin care products. Several thousand chemicals are found in formulations of these products. Barbers generally cut only men's hair and make limited use of some of the above products, such as hair dyes, in their work.

Hair colourants are classified as permanent (primarily aromatic amines and aminophenols with hydrogen peroxide), semi-permanent (nitro-substituted aromatic amines, aminophenols, aminoanthraquinones and azo dyes) and temporary (high-molecular-weight or insoluble complexes and metal salts, such as lead acetate). The numerous individual chemicals used in hair colourants have varied over time. Only permanent and semi-permanent hair colourants are used to a significant extent by hairdressers, while consumers at home use any of the three types.

Hairdressers may also be exposed to volatile solvents, propellants and aerosols (from hair sprays), formaldehyde (an antibacterial agent), methacrylates (in nail care products) and trace quantities of nitrosamines, which have been reported in many hair care products.

It is estimated that there are several million hairdressers and barbers worldwide. Few exposure measurements are available. Approximately 35% of women and 10% of men in Europe, Japan and the USA use hair colourants.

5.2 Human carcinogenicity data

There is consistent evidence from five (all from Europe) of the six large cohort studies of an excess risk for cancer of the urinary bladder in male hairdressers and barbers. The increase was significant in three studies, and the overall risk relative to that in the general population amounted to about 1.6. In 12 case-control studies, male hairdressers and barbers had an overall relative risk of about 1.2; smoking was adjusted for in three of these case-control studies, conducted in North America, and these did not show an overall excess risk. The risk for cancer of the urinary bladder was less consistently increased in corresponding studies in women: positive results were obtained in five cohort studies and negative results in three; none was significant. An overall relative risk for lung cancer of about 1.3 was seen among male and female hairdressers in cohort studies. One case-control study from Australia found a significant excess risk for non-Hodgkin's lymphoma among female hairdressers; a nonsignificant excess of this malignancy was noted in one cohort study from Denmark in men and women and in one case-control study from the USA in men.

One cohort study, from Finland, found a significant excess risk for ovarian cancer; two other studies, in the USA and Japan, found nonsignificant risks, and a fourth, in Switzerland, showed no effect. Excess risks were seen among male hairdressers for cancers of the buccal cavity and pharynx and prostate in one study from Switzerland; increased risks for cancers at these sites were not reported in another cohort study, from the United Kingdom.

Personal use of hair colourants has been studied in seven case-control studies of cancer of the urinary bladder. Overall, these do not indicate an excess risk; however, one study from Denmark found an association with personal use of brilliantine, although it had methodological limitations. Following a report in 1976 of an excess of breast cancers among hair dye users in New York, USA, six case-control studies and one cohort study examined this subject. None found evidence of a significant excess among hair dye users overall. One case-control study of non-Hodgkin's lymphoma from Iowa and Minnesota showed a significantly increased risk among male users of hair colouring products. A second case-control study, from Nebraska, showed an excess risk for this malignancy among female users of hair colourants but showed no excess among a smaller number of male users. The case-control study from Nebraska also found a significant excess of multiple myeloma among female users of permanent hair dyes, and another study from Iowa reported a nonsignificant excess of this malignancy in male users of hair colourants. One cohort study in the USA showed no excess risk among hair dye users for all lymphomas combined. One case-control study of neuroblastoma and one of Wilms' tumour showed significantly increased risks for the offspring of mothers who had used hair dyes during pregnancy. Single studies have reported significant excess risks for Hutchinson's melanotic freckle, Hodgkin's disease, leukaemia, malignant tumours of the brain and cancers of the salivary gland, cervix and lower female genital tract. Other studies showed no such excesses.

The higher prevalence of smokers reported among male hairdressers and barbers in some studies is consistent with the overall excess of lung cancer but cannot readily explain the magnitude of the increase in risk for cancer of the urinary bladder in the European cohort studies. In particular, studies in Switzerland and Denmark have shown significant excesses of cancer of the urinary bladder unaccompanied by appreciable excesses of lung cancer, which further weigh against smoking as the sole explanation for the overall excess. Specific exposures of hairdressers and barbers have not been evaluated in epidemiological studies.

5.3 Animal carcinogenicity data

Various commercially available hair dye formulations and various laboratory preparations of hair dyes were tested for carcinogenicity in mice or rats by skin application in many studies and by subcutaneous injection in a single study in rats. In one study by skin application in rats, a particular formulation was associated with an increased incidence of pituitary adenomas in females. The other studies either showed no increased incidence of tumours at any site or were inadequate for evaluation.

5.4 Other relevant data

Contact dermatitis is a common clinical dermatological problem in hairdressers. Because hairdressers use a wide variety of multicomponent chemical products, it is difficult to determine the specific etiology of their dermatitis, although cutaneous nickel allergy and atopic status have been suggested to play a role. Moreover, many of the products used contain both irritants and sensitizers. Pulmonary toxicity has been associated with the use of hair lacquer by consumers and hairdressers.

No study has reported a significant excess of congenital malformations, early or late fetal death or low birth weight among the offspring of male or female barbers or hairdressers.

No increase was observed in chromosomal aberration frequencies in the lymphocytes of humans exposed to commercial hair colourants which included hydrogen peroxide application. In this and another study, no increase in sister chromatid exchange frequency was found.

A number of different commercial permanent and semipermanent hair colourants were tested for their mutagenic activity in vitro. Many were mutagenic to bacteria. Less than half of the preparations applied to rats resulted in the excretion of bacterial mutagens in urine. Application of a semipermanent and an oxidation dye colourant topically to male rats had no effect on the reproductive performance of the treated rats and did not induce heritable translocations, as judged by a mating protocol.

5.5 Evaluation

There is limited evidence that occupation as a hairdresser or barber entails exposures that are carcinogenic.

There is inadequate evidence that personal use of hair colourants entails exposures that are carcinogenic.

Overall evaluations

Occupation as a hairdresser or barber entails exposures that are probably carcinogenic (Group 2A).

Personal use of hair colourants cannot be evaluated as to its carcinogenicity (Group 3).

For definition of the italicized terms, see Preamble Evaluation.

Last updated 08/22/1997

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