A new objective skin colour scale for research and clinical practice

A collaboration of scientists from the UK, USA, Australia, and France have proposed a more objective and detailed way to describe the huge variety of skin colour, called the Eumelanin Human Skin Colour Scale (EHSCS) and measured with a simple colourimeter.

Current systems and terminology for general classification of skin colour are inadequate, subjective, exclusionary or just incorrect, and hamper our efforts to research and treat diseases of the body’s largest organ.

Skin colour has important effects on the skin diseases you are prone to, how to diagnose them, and what treatment is appropriate, but we don’t have a good way of describing skin colour for doctors and researchers. Most scales were developed for European skin and later expanded, but still short-change the depth of skin variety. Ethnicity is important – for example, Han Chinese people are more prone to Stevens-Johnson syndrome, a life-threatening skin disease that requires immediate, intensive treatment – but ethnicity or population-group markers don’t precisely describe skin colour and shouldn’t be used as a marker for it. Check out the image of the Black members of the 2018 US Congress to see the diversity of skin colour that can be covered by a single, generic designator.

Skin colour measurement has wider implications that just skin diseases. The COVID-19 pandemic highlighted that pulse oximeters, a simple but critical tool to determine when patients are not getting enough oxygen, give higher oxygen readings for people with darker skin colours. Pulse oximeters work by shining a light into a fingertip and measuring the amount of light absorbed by the haemoglobin in the finger as a proxy for oxygen levels – higher light absorption means higher blood oxygen levels. But these were developed and tested on white skin. The melanin in dark skin also absorbs light, resulting in an inaccurate reading. This misleads doctors into delaying supplementary oxygen for these patients, which can have profound effects on a patient’s outcome. A measurable eumelanin index could be used to adjust oximeter readings to reflect the true blood oxygen level and ensure that people with darker skin are not being under-treated in such a critical area.

The Fitzpatrick scale has been used as a default skin type scale used in Australia, the USA and Europe, but it was actually designed as a measure of how easily you sunburn and tan, not skin colour. These are two related but not identical features of skin. The Fitzpatrick scale was initially designed for lighter skin types and, although it was later expanded to include darker skin colours, doesn’t account for the huge variety of non-European skin colours. Instead, the multidisciplinary Dermatological Lexicon Group have proposed a measurement of melanin, the main pigment in the skin, with a tool called a colourimeter, to accurately describe skin colour. 

The EHSCS is divided into a five-point descriptive scale based on eumelanin in a variety of human populations, ranging from Ireland to Ghana. Eumelanin is the black-brown pigment that, in different amounts, produces the amazing variety in human skin colours and is measured with a simple colourimeter by the amount of light reflected from the skin. The word eumelanin also has no pejorative connotations, something that is all too common in discussions surrounding skin colour.

University of Queensland.