Date: 10/04/2022

Dr Ophelia Dadzie

Published -

04/Oct/2022

Historically, the practice of Western dermatology has been embedded in Eurocentrism, with the discipline primarily being studied and developed in Europe, using terminology that fits only a portion of the variety of human skin colours that exist. At present, there is no standard terminology for describing the spectrum of constitutive skin colours across human populations. Skin colour, however, has an impact on the skin diseases someone may be prone to, their diagnosis, and the available treatments for each.

Considering the above, we developed an objective way to describe the huge variety of human constitutive skin colours, called the Eumelanin Human Skin Colour Scale (EHSCS), a collaborative effort of scientists from the UK, USA, Australia and France.

The description of this scale as ‘objective’ is important, especially in clinical practice. Up until now, the default terms and scales used in dermatology to describe human skin colour have been imprecise, subjective and not grounded in science, e.g. “white” or “black” skin, “skin of colour” and/or “ethnic skin”. Furthermore, the Fitzpatrick Skin Classification System which is currently widely mis-used in clinical practice as a de facto classification of human constitutive skin colour, was not created for this purpose. Instead, it was developed as a subjective sun reactivity scale that focuses primarily on the range of variation observed in European populations with more lightly pigmented skin.

The EHSCS is a new, objective scale for classifying and describing human constitutive skin colour. It is based on melanin index (MI), which reflects the amount of melanin (specifically eumelanin) in the skin. Melanin Index is determined by the way a person’s skin reflects light of pre-determined wavelength(s) and is measured using a skin reflectance instrument.

We created the EHSCS by reviewing published data for MI for indigenous human populations, from Ghana to Ireland. By focusing on the MI values at the extremes of human constitutive skin colour, we were able to define the range of the mean MI values for indigenous human populations and split the MI distribution into five categories.

We developed associated lexicon for each of the five categories that is based on the word “Eumelanin”. Eumelanin is the pigment that determines a person’s skin colour. Everybody has eumelanin in their skin, just in differing amounts. The word eumelanin is also a neutral word, meaning the language associated with our scale is as non-pejorative as possible. The five categories of our EHSCS and their associated MI cut-off points are listed below:

• Eumelanin Low :<25
• Eumelanin Intermediate Low: 25-<50
• Eumelanin Intermediate: 50-<75
• Eumelanin Intermediate High: 75-<100
• Eumelanin High: ≥100

From the times I have used the EHSCS in clinic, I have had encouraging results, enabling me to objectively evaluate and describe the constitutive skin colour of my patients.

For example, I recently assessed a 24-year-old woman of Indian origin in my clinic. Both her parents and grandparents were of Indian (specifically Punjabi) ancestry. On visual inspection she was lightly pigmented, had dark brown hair and green eyes. Under common terminologies used in Dermatology she would have been categorised as being a person with “skin of colour” or having “ethnic skin”, primarily because of her ancestral origin. Using a skin reflectance instrument to determine her constitutive MI, I determined her constitutive skin colour was in the category of Eumelanin Low (MI=21). Exploring the issue of sun reactivity with the patient, she reported that she burned easily and tanned poorly (Fitzpatrick Skin Phototype 2). In terms of genetics of skin pigmentation, it may be that she has a history of admixture in her distant ancestors (the major OCA2 non-brown eye/lighter skin colour associated SNP is found in the Indian population), or possibly even an albinism allele carrier that has been associated with lighter eye/skin colour. Nevertheless, this case highlights the variability of skin colour in human populations and the limitations of terminologies such as “skin of colour” and/or “ethnic skin”.

My clinic has the skin reflectance instrument needed to be able to incorporate the EHSCS into my clinical practice. However, we are all aware there are currently limitations to the widespread use of this scale. Without the skin reflectance instrument, doctors cannot use the EHSCS routinely in clinical practice, making it more suitable for the research setting at present.

Luckily there is hopeful news on the horizon: our group are in the process of developing an associated skin colour matching chart for the EHSCS, which will enable clinicians to determine a person’s EHSCS without the use of a skin reflectance instrument.

The ability to objectively determine and describe a person’s constitutive skin colour is a game-changer in our field, especially if it can be easily incorporated into clinical practice.

Acknowledgements:

We would like to thank Professor Rick Sturm for his comments and intellectual contribution to this insight in relation to the possible genetics underlying the case of the 24-year-old woman of Indian ancestry discussed in the above post.