Melasma area and severity index (MASI). A area, D darkness, H homogeneity
MASI total score =
0:3 × A (forehead) × (D + H) (forehead) +
0:3 × A (left malar) × (D + H) (left malar) +
0:3 × A (right malar) × (D + H) (right malar) +
0:1 × A (chin) × (D + H) (chin)
The MASI score range from 0 to 48, with 48 being the most severe. At first glance, the advantages of the MASI score is obvious as it takes into account both the area of involvement as well as the degree of pigmentation, two of the most important components that affects the patients adversely. In addition, as the MASI is a continuous score, it reflects changes much better than the old melasma severity scale, which is a categorical scale.
The MASI score has also been validated recently in a prospective study by Pandya, et al. . In the study, the MASI score shows good reliability within raters on different days as well as between raters. It is important to note that all raters who participated in the study had some training and were given examples of different levels of area, darkness and homogeneity in aiding their scoring. This probably accounted for the consistency observed both within rater and inter-raters. The MASI scores were also compared with Mexameter readings as well as with melasma severity scale and showed good validity.
In actual practice, however, the MASI has its drawbacks. Firstly, consistency is difficult to achieve as MASI is based on subjective visual assessment of the three components of area of involvement, darkness and homogeneity which results in inter-assessor variability. Secondly, while the MASI score is a continuous score, the three components of area, darkness and homogeneity assessed are grouped in bands. This is not ideal as significant changes within each band will not be reflected, while small changes across bands result in a significant change in scores. Finally, MASI is rarely used outside clinical trials due to the complexity of calculations and is time-consuming in nature. As a result, modifications to the score have been made resulting in the simpler modified MASI score.
8.4 Modified Melasma Area and Severity Index (mMASI)
The modified melasma area and severity index (mMASI) was proposed by Pandya et al.  in 2011 after the team did a validation of the MASI score. In the study, despite training of the raters and providing them with examples of the different scales in the components of area, darkness and homogeneity, the study team still found assessing the different components of MASI problematic, particularly in the assessment of homogeneity. As such, the team proposed a modified MASI system with the removal of homogeneity component. In their study, removal of the homogeneity component did not affect the reliability or validity measures at all  and the authors suggested the removal of that component would result in a simpler, easier and more consistent scoring system. The modified MASI score is therefore calculated in the following manner:
Modified MASI total score =
0:3 × A (forehead) × D (forehead) +
0:3 × A (left malar) × D (left malar) +
0:3 × A (right malar) × D (right malar) +
0:1 × A (chin) × D (chin)
In addition, in order to improve consistency in assessment of the two components of area and darkness, the authors proposed that a training module as well as practice images be given so as to ensure reliability in mMASI scores. Since the introduction of mMASI in 2011, it has replaced MASI and is used in almost all of published clinical studies assessing treatment options for melasma. While the removal of the homogeneity component does help in making the mMASI simpler to perform, it still does not address the problems associated with MASI, which are mainly banding within the scale of each component, inter-observer variability and the need for training to ensure reliability. As such, a better scoring system is still needed to overcome the observed problems.