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In Reply: We agree with Drs Zahm and Fraumeni that the meta-analysis process is limited by the information provided in the individual studies. If data are available in only 1 or 2 studies, it may be difficult to include them in a meta-analysis. This is why we did not claim that our meta-analysis was conclusive about the potential carcinogenic effect of hair dyes and called for further studies.

Zahm and Fraumeni mention 5 individual ORs for dark colored dyes, but they provide the corresponding 95% CI only for Zhang et al (OR, 2.1; 95% CI, 1.0-4.0).¹ The 95% CI corresponding to the OR of 2.1 from the study by Altekruse et al² is 0.7 to 6.7 and is based on only 3 exposed cases. The OR for black hair coloring in the study by Zahm et al³ is 4.1, but its 95% CI is 0.9 to 18.8 (representing 4 cases), . . . [Full Text of this Article]

Bahi Takkouche, MD, PhD
mrbahi@usc.es

Agustín Montes-Martínez, MD, PhD
Department of Preventive Medicine
University of Santiago de Compostela
Santiago de Compostela, Spain

Mahyar Etminan, PharmD, MSc(Epid)
Division of Clinical Epidemiology
Royal Victoria Hospital
Montreal, Quebec