Colorimetry provides a rapid objective measurement of de novo hair growth rate in mice

Background: Depilated mice have been used as a test platform for hair growth-regulating agents. However, currently available assessment tools for hair growth in mice are less than ideal. Methods: Tristimulus colorimetry of the fur color of depilated agouti, albino, and black mice with L^*, a^*, and b^* values were performed daily until the full growth of pelage. Using light-emitting diode (LED) irradiation (650 and 890 nm) with a daily dose of 3.5 J/cm² as hair growth regulators, the hair growth rates observed by the global assessment were compared with those derived from colorimetry. Results: In contrast to a^* and b^* values, L^* values changed more drastically over time in the anagen phase regardless of fur color. Unlike the inhibitory effect of 650 nm irradiation, LED of 890 nm promoted de novo hair regrowth in mice. The difference in hair growth rates detected by colorimetry paralleled the observation made by the global assessment. Conclusion: The L^* value of fur color obtained by tristimulus colorimetry was a sensitive yet quantitative indicator of de novo hair growth, and could be used to project the hair growth rate in mice.