Toxicity of hair dyes in experimental <i>in vivo</i> animal models: a systematic review

Twenty-five articles were included. The evidence indicated multifactorial toxicity affecting cardiac, hepatic, renal, testicular, respiratory, dermatological, hematological, genotoxic, hormonal, and developmental endpoints. However, relevance varied according to exposure route, dose, species, model, publication period, and whether the tested material was an isolated ingredient or complete formulation.

Topical studies were the most relevant to cosmetic exposure, whereas oral, subcutaneous, intravenous, and embryo immersion models primarily supported hazard identification under non-usual or high-bioavailability conditions. SYRCLE assessment showed a predominance of unclear risk of bias, with methodological weaknesses in nearly all studies. Hair dye ingredients and finished formulations can produce toxicological hazard signals under specific experimental conditions.

Nevertheless, these findings should not be interpreted as direct estimates of real-world consumer risk. More standardized, exposure-relevant, and robust studies are needed to improve hazard characterization and support risk interpretation, particularly for occupational exposure scenarios.</p>