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Are Coal-Tar Shampoos Safe?

Polycyclic aromatic hydrocarbons (PAHs) are one type of hundreds of compounds found in coal tar. Based on the knowledge that exposure to PAHs is associated with an increased cancer risk, these researchers sought to determine whether coal-tar shampoos contribute to the PAH "body burden." Eleven healthy participants washed their hair with a coal-tar shampoo for 30 seconds twice in succession. Urine was collected on the day before the shampooing and on the following two days for measurement of 1-hydroxypyrine (1-OH-P), a PAH metabolite. The mean increases in totally excreted 1-OH-P on the first and second days after shampooing were 10 and 5 times the background values, respectively. The 1-OH-P values on day 1 were similar to those found in coke-oven workers at the end of a 7-day working period.

Comment: The finding that the urine concentration of carcinogenic PAH was as high in these subjects one day after shampooing as it is in coke-oven workers after seven days of work is, at first glance, extremely worrisome, especially given that coke oven workers have an increased rate of death from respiratory cancer. However, several observations render the significance of these results less clear. First, despite decades of use of coal-tar shampoos, especially in patients with psoriasis, there have been no reports of an increased incidence of respiratory cancer in these persons. Second, the shampoo that the researchers used has a PAH concentration at least 100 times higher than that of seven other commercially availa-ble coal-tar shampoos they evaluated. Still, the results of this study are cause for concern, and two questions the authors pose are worth repeating: Should coal-tar shampoos be sold without prescription? and, Should a limit be set for PAH in these shampoos? The answers are not yet known.

— JS Dover

Published in Journal Watch Dermatology February 1, 1995

Citation(s):

van Shooten F-J et al. Dermal uptake of polycyclic aromatic hydrocarbons after hairwash with coal-tar shampoo. Lancet 1994 344 1505-1506.

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