Final Report on the Safety Assessment of t-Butyl Hydroquinone

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The original safety evaluation of t-Butyl Hydroquinone (J. Am. Coll. Toxicol. 5(5), 1986) concluded that data on the depigmentation potential of this ingredient were required before it could be concluded that this ingredient is safe for use in cosmetic products. The safety test data included in the original 1986 evaluation are summarized in this report. The data indicated that t-Butyl Hydroquinone was slightly toxic in oral feeding studies but was neither a human irritant nor sensitizer when tested at 0.14%. The results from subchronic, chronic, and teratogenic studies of t-Butyl Hydroquinone and hair dyes containing this ingredient were unremarkable. The required new data included in this addendum to the original report indicate that t-Butyl Hydroquinone was a weak depigmentor at 1.0 and 5.0% but not at 0.1%. Although a threshold for depigmentation was not established, the dose-response relationship was adequate to conclude that t-Butyl Hydroquinone at concentrations of use of 0.1% and less would not be a human depigmentor. Other data indicated that this ingredient was not a phototoxic agent. Therefore, the conclusion in the original report is amended to conclude that t-Butyl Hydroquinone may be safely used as a cosmetic ingredient at concentrations not to exceed 0.1%.