A, Higher melanin index (MI) values represent darker pigmented skin, whereas lower individual typology angle (ITA) values represent darker pigmented skin. The MI and ITA values demonstrate a strong negative correlation. B, Frequency of participants by spectrophotometer-derived Del Bino skin type category (ITA) and Fitzpatrick skin type (FST) derived from a pigment-measuring device. These unrelated classification systems demonstrate a strong correlation.
Wilkes M, Wright CY, du Plessis JL, Reeder A. Fitzpatrick Skin Type, Individual Typology Angle, and Melanin Index in an African PopulationSteps Toward Universally Applicable Skin Photosensitivity Assessments. JAMA Dermatol. 2015;151(8):902-903. doi:10.1001/jamadermatol.2015.0351
Calculation of the individual typology angle (ITA) based on spectrophotometric measurements has been used to classify skin types into 6 physiologically relevant groups: very light, light, intermediate, tan, brown, and dark.1,2 This study directly compares ITA values with the melanin index (MI), which is frequently used in assigning Fitzpatrick skin type (FST),3 to improve understanding of how these measurements correlate when used in a study that primarily includes participants with FSTs V and VI.
Participants (N = 556) were drawn from the Council for Scientific and Industrial Research campus in Pretoria, South Africa, from October 6 through 22, 2014. The research ethics committee of the Council for Scientific and Industrial Research approved the protocol. All participants provided written informed consent, spoke English, cleaned their nondominant arm with a sanitary wipe, and answered a short questionnaire in which they self-identified their population group and skin reaction to sunlight. We determined the ITA and MI objectively using commercially available devices (Skin Colorimeter CL 400 and Mexameter MX 18 [Courage+Khazaka Electronics, GmbH], respectively) by holding the devices against the inner part of the upper nondominant arm. We categorized ITA as previously described.1 The following FST and MI values were found: FST I for an MI of 0 to 99.9, FST II for an MI of 100.0 to 149.9, FST III for an MI of 150.0 to 249.9, FST IV for an MI of 250.0 to 349.9, FST V for an MI of 350.0 to 749.9, and FST VI for an MI of 750.0 or greater. We used commercially available statistical software (STATA, version 10.0; StataCorp) for data analysis.
The 556 participants self-identified race/ethnicity as black (n = 390), Indian/Asian (n = 51), white (n = 99), or colored (mixed race/ethnic group) (n = 16). Because the current procedure for assigning FST relies on perception of how skin burns and/or tans, participants identified whether their skin (1) burned without tanning, (2) burned and then tanned, or (3) only tanned after initial sun exposure. Participants from every ethnic group related to the different tan/burn options and demonstrated some level of sun photosensitivity even in ethnic groups frequently associated with darker skin pigmentation (Indian/Asian, black, and colored) (Table).
We compared our questionnaire findings with objective skin measurements and found that participant MI readings and ITA measurements demonstrate a very strong negative correlation (Spearman ρ = −0.98; P < .001) (Figure, A). As ITA values decreased, MI values increased monotonically. We then analyzed how these measurements correlated after raw values were categorized. Although ITA and MI values place individuals into 1 of 6 skin types, these classification systems are currently unrelated, with no consensus about which MI values belong to which FST group.4,5 We found that by placing participants with MI values of 750.0 or greater in FST VI, we observed a very strong correlation between these unrelated classification systems (Spearman ρ = 0.95; P < .001) (Figure, B).
Determining skin type is necessary for understanding personal risk for sunburn and, by extension, skin cancer. Skin type is also important clinically because the cosmetic and medical industries have increased their use of laser applications in recent years.6 Because questions about FST are used to assign skin type and determine laser-based treatment variables, participants were asked questions about FST, and 538 (96.8%) stated that the sun affected their skin in some way. Of the 390 black participants, 373 (95.6%) acknowledged that they were photosensitive (Table). Only individuals who are not photosensitive are typically classified as FST VI, and our data confirm that most black participants should be classified as having an FST other than VI.3 As a result, we defined the MI for FST VI to include only individuals with an MI of 750.0 or greater. Strong correlation between MI and ITA values (Figure) suggests that either of these methods can be used to assess skin pigmentation depending on the relevance of the measurement outcome of the intended study. Recognizing this strong correlation will allow research by health care professionals, biomedical scientists, and public health researchers to be more applicable and comprehensible across disciplines.
Accepted for Publication: February 7, 2015.
Corresponding Author: Marcus Wilkes, BS, Baker Laboratory, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853 (firstname.lastname@example.org).
Published Online: April 29, 2015. doi:10.1001/jamadermatol.2015.0351.
Author Contributions: Mr Wilkes and Dr Wright had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.
Study concept and design: Wilkes, Wright, du Plessis.
Acquisition, analysis, or interpretation of data: Wilkes, Wright, Reeder.
Drafting of the manuscript: Wilkes, Wright, Reeder.
Critical revision of the manuscript for important intellectual content: All authors.
Statistical analysis: Wilkes, Wright.
Obtained funding: Wilkes, Wright.
Administrative, technical, or material support: Wright.
Study supervision: Wright.
Conflict of Interest Disclosures: Mr Wilkes is a doctoral student at Cornell University supported by a National Science Foundation Graduate Research Fellowship. Dr Wright was employed by the Council for Scientific and Industrial Research (CSIR) in South Africa. Dr Reeder is a member of the National Health Promotion Advisory Committee, Cancer Society of New Zealand, Inc.
Funding/Support: This study is supported by grant NSF DGE-1144153 from the National Science Foundation Graduate Research Fellowship Program (Mr Wilkes); by an international travel allowance cofunded through the Graduate Research Opportunities Worldwide and US Agency for International Development agencies; by CSIR Parliamentary Grant funding (Dr Wright); by the National Research Foundation Rated Researcher funding (Dr Wright); by an ad hoc grant from the Cancer Association of South Africa (Dr Wright); by the Cancer Society of New Zealand, Inc (Dr Reeder); and by the University of Otago (Dr Reeder).
Role of the Funder/Sponsor: The funding sources had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.
Disclaimer: Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation or the National Research Foundation.
Additional Contributions: We thank the participants in this study.
Correction: This article was corrected on August 12, 2015, to fix statistics in the Figure.