Physical measurement and evaluation of skin color changes under normal condition and post-ultraviolet radiation: a comparison study of Chromameter CM 2500d and Maxmeter MX18.

Objective: To compare the data correlation between two kinds of instruments, Chromameter CM2500d and Maxmeter MX18, in the measurement of skin color changes under normal condition and post-ultraviolet (UV) radiation. Method: The data points of Chromameter CM2500d are based on L*a* values, while Maxmeter MX18 are based on M and E values, in order to compare the data correlation between these two kinds of instruments in skin color measurement on both non-exposed and exposed sites. In addition, an evaluation of the correlation of post-UV irradiation between these two instruments was conducted. Four different kinds of parameters post-UV radiation were measured including minimal erythema dose (MED), immediate pigmentation dose (IPD), minimal persistent pigmentation dose (MPPD) and repeated UV radiation. The following UV radiation dosages were applied as Day 1=1.0 MED, Day 2=0.5 MED and Day 3=0.5 MED for repeated UV radiation, of which the erythema and pigmentation changes were recorded. Result: Chromameter CM2500d and Maxmeter MX18 showed good data correlation when measuring both non-exposed and exposed sites on normal skin. L* values were affected more easily by UV-induced erythema than M values on skin color changes after 1 MED and repeated UV exposures. IPD, MPPD and the pigmentation data showed good correlations with the measurement of the intensive erythema formation induced by repeated UV exposures. a* value was shown to be equally effective as E value with skin erythema measurements in response to various MEDs. However, increased erythema induced by repeated UV radiations was able to reduce the correlations between a* and E values. On the other hand, a* and E were shown to be equally effective in recording the erythema change courses after strong erythema responses post-UV radiations. Conclusion: This comparative study showed that the data correlations between the two kinds of instruments were different depending on measurement conditions. Both Chromameter CM2500d and Maxmeter MX18 instrumental measurement results should be carefully evaluated by experimental conditions.