Happy kids in minimal dress Diversity in skin tones
| Photo Credit: Freepik

A pulse oximeter is placed in the hand of a COVID-19 patient. A team of researchers from the University of Nottingham (UoN) have developed a laboratory-based test to assess the performance of POs under the effects of varying melanin (pigment responsible for colour) concentration and oxygen saturation (SpO2) values.
| Photo Credit: File photo

Given that the performance of pulse oximeters (POs) is known to vary with the colour of skin, a team of researchers from the University of Nottingham (UoN) have developed a laboratory-based test to assess the performance of POs under the effects of varying melanin (pigment responsible for colour) concentration and oxygen saturation (SpO2) values.

A study pertaining to this, titled ‘Pulse oximeter bench tests under different simulated skin tones’, has been published in Medical and Biological Engineering and Computing, a peer reviewed medical journal.

Pulse oximeters were the most commonly used devices during the covid pandemic as they allowed for non-invasive, painless, continuous and inexpensive real-time monitoring of oxygen levels in the blood using light (commonly, red and infrared light).

Need for caution

Suvvi K. Narayana Swamy, lead author of the study, told The Hindu that POs did not show any deviations in SpO2 readings due to skin colour in the laboratory tests. “However, the tests also did not conclusively demonstrate that melanin does not affect SpO2 measurements. So, we need to be cautious not to over interpret these results. Further research is underway,” she said.

“In the United Kingdom, the COVID Oximetry @home programme was launched as part of the National Health Service (NHS) response to the pandemic. Through this programme, commercially available peripheral POs were delivered to allow patients with COVID-19, or at high risk, to remotely monitor their SpO2 levels at home. These devices were widely used globally by healthcare professionals to make timely clinical decisions when admitting patients (particularly with the absence of any noticeable symptoms) to hospitals for critical care and treatment,” Ms. Swamy said.

The study gains significance in a context where several recent retrospective clinical studies have highlighted that SpO2 may be overestimated in patients with non-white skin types. This phenomenon is generally termed occult hypoxemia, where SpO2 measured by a PO is greater than 90%, despite true oxygen saturation value being less than 88%,” she explained. 

“In this study, the performance of POs used in the NHS COVID Oximetry @home programme and in hospitals in UK was investigated. The test enabled the POs to be subjected to low signal and varying melanin concentration, which are the two main principal effects of melanin in the skin through simulation. The effects of low signal levels were simulated by neutral density filters (NDFs) that reduced red and infrared radiation light in the same manner while the effects of melanin concentration were achieved by utilising melanin filters (MFs) that decreased both red and IR light by unequal amounts.In these tests, the SpO2 overestimation, which has often been observed clinically, was not reproduced,” she explained.

Significant variations

Stating that a laboratory simulation was used to mimic different SpO2 values (~ 70 to 100%), Ms Swamy said different neutral density and synthetic melanin filters were used to reproduce low signal and varying melanin reduction levels. “POs from six different brands were reviewed and their response documented. Significant variations were observed in the recorded SpO2 values among different POs when exposed to identical simulated signals.  Differences were greatest for lower SpO2 (<80%) where empirical data is limited,” Ms. Swamy said.

“All PO responses under low signal and melanin concentration did not change across various simulated SpO2 values. The tests do not provide conclusive evidence that melanin does not affect in vivo SpO2 measurements. Research in the areas of instrument calibration, theory and design needs to be further developed,” she added.

A video of Prime Minister Narendra Modi criticising Sam Pitroda, the former chairman of the Indian Overseas Congress, over alleged racist remarks, has been altered and shared to falsely claim that Modi called President Droupadi Murmu dark skinned.

In a May 2, 2024, interview with The Statesman, Pitroda while trying to give an analogy for India’s diversity said that people from different regions of India resemble Chinese, Arab, White, and African races. He emphasised that despite these differences, Indians have lived together harmoniously for 70-75 years. After this interview, Pitroda was criticised for his remarks, and the Congress party distanced itself from his comments. On May 8, Congress leader Jairam Ramesh announced that Pitroda had resigned from his position in the Indian Overseas Congress.

In 15 seconds video, Modi can be heard saying, “Those who have black skin, they are all from Africa. Droupadi Murmu is also African, and because she has dark skin that’s why she should be defeated”.

The viral video is also being shared on Facebook with the same false claim.

FACT-CHECK

BOOM found that the viral video has been cropped from a longer video of Prime Minister Narendra Modi’s speech and has been doctored to change its meaning. In the full speech, Modi criticised Sam Pitroda for alleged racist remarks and claimed that Congress opposed President Droupadi Murmu’s candidature because of her skin color. The viral clip has been culled from a video posted on May 8, 2024 by BJP’s official YouTube channel. From the 44 minutes timestamp, Modi can be heard saying, “I got to know that there is an uncle in America who is the philosophical guide of ‘Shehzada’ and just like the third umpire in cricket this ‘Shehzada’ takes advice from the third umpire. This philosophical uncle said that those who have black skin are from Africa. This means that you are abusing several people in the country on the basis of their skin colour.”

The viral clip has been culled from a video posted on May 8, 2024 by BJP’s official YouTube channel. From the 44 minutes timestamp, Modi can be heard saying, “I got to know that there is an uncle in America who is the philosophical guide of ‘Shehzada’ and just like the third umpire in cricket this ‘Shehzada’ takes advice from the third umpire. This philosophical uncle said that those who have black skin are from Africa. This means that you are abusing several people in the country on the basis of their skin colour.” “Then I understood, that looking at the color of the skin, they (Congress) assumed that Droupadi Murmu is African, and because her skin color is black, that’s why we (Congress) should defeat her,” he further alleged.

The part before this has been edited out of the viral video to make the false claim that Modi called Murmu dark skinned. The full speech can be seen here.

(This story was originally published by BOOM, and republished by NDTV as part of the Shakti Collective)

(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)

Students of a school in Rameswaram, Tamil Nadu, wave at the camera, April 18, 2018.
| Photo Credit: Church of the King/Unsplash

Skin, with its wide spectrum of textures, hues, and histories, has long captivated the imagination of poets and storytellers. It has served as a canvas for the expression of beauty, identity, and cultural symbols. The diversity of skin colour across human populations is a product of human genetics, the migration of peoples, and the complex interplay between genes and the environment.

Together with its colour, skin opens a window into the underlying human pathophysiology, and not just because it’s the largest organ, and has as a result been the subject of many scientific and medical investigations as well. The natural colour of human skin and changes therein help clinicians diagnose a number of medical conditions. For example, genetic defects can result in the absence of pigmentation by birth, such as albinism; partial or complete depigmentation can also result in disorders like vitiligo. A number of drugs, including antimalarials and chemotherapy agents, also cause skin pigmentation.

But for all of skin’s significance and wonder, its colour has also been the basis of social hierarchies, racism, and other forms of discrimination. Recognising the biological basis of skin and celebrating the diversity of skin colour could instead foster a deeper appreciation of human differences and promote inclusivity.

What is the effect of ultraviolet radiation?

The pigment melanin determines the colour of skin. It is produced by cells called melanocytes. A number of genes and factors influence the type and size of melanin particles as well as its production, transport, and distribution.

Scientists widely believe exposure to ultraviolet light from the Sun has been the dominant driver of skin colour throughout history. Across geographies, colours have also displayed a close connection to the latitude, which in turn is correlated with ultraviolet exposure. There is also consensus that lighter skin colour across higher latitudes is the result of humans adapting to produce vitamin D — again, a process induced by ultraviolet light. Skin pigmentation also protects nutrients like folate from being broken down by ultraviolet radiation.

This said, systematic approaches to understand and document skin colour have been only of recent interest. In 1735, the Swedish biologist Carl Linnaeus classified humans into four ‘varieties’ based on skin colour. The Austrian anthropologist and explorer Felix von Luschan designed a scale with which to compare skin colour in the 19th century. The scale has 36 colours and is used to this day.

Dark-skinned humans evolved from apes around 1.2 million years ago by shedding body hair and adapting to ultraviolet radiation. Skin colour is also one of the more striking phenotypes (attributes produced by genes’ interactions with the environment) in humans, being closely related to their migration and adaptation as they moved out of Africa around 100,000 years ago.

Researchers have found genes associated with the melanocortin 1 receptor, a protein associated with the creation of light skin, in the DNA of Neanderthals from Spain and Italy but not from Croatia, and not in Denisovans.

Which genes are involved in skin colour?

As for modern-day human skin colour: the prevailing hypothesis is that it’s the result of natural selection across a few genes. Two of these, SLC24A5 and SLC45A2, are the most well-studied. They affect skin colour in modern Eurasians. Other genes like MC1R, TYRP1, and OCA2 affect that of East Asians. And all of them show signals of natural selection.

Researchers widely believe Europeans and East Asians adapted to have lighter skin through independent processes. Some evidence has been found for natural selection in Europeans around 11,000-19,000 years ago. A 2015 study led by Harvard Medical School, together with several international organisations, suggested Europeans became mostly light-skinned by at least 4,000-6,000 years ago. Later, the admixture of global populations plus local adaptations resulted in the large diversity of skin colour we observe today.

There are many exceptions to this general rule, however. For example, the Inuit people who have inhabited Alaska for more than five centuries, have darker yellowish brown skin compared to other populations at the same latitude. This has been a puzzling exception for many years. Researchers have hypothesised a high vitamin D intake and high ultraviolet exposure due to longer days have combined to create this anomaly.

How does skin colour vary?

Human genetic conditions like albinism — which results in partial or complete loss of pigment of the skin — provide insights into the biology of skin pigmentation and how society addresses people with rare conditions. Around one in 20,000 individuals around the world are estimated to have this condition, but the prevalence could be 20-times higher among the Tonga people of Africa and 120-times higher among the Guna people of South America. Individuals with albinism are highly predisposed to developing skin cancers, not to mention also having to suffer regressive social attitudes.

The latest advances in genomics are improving our understanding of the biology of skin pigmentation. In a paper published in the journal Nature Genetics in January 2024, researchers at the University of Pennsylvania used genome editing and chromosomal conformational capture to identify the regulators of a number of genes involved in skin pigmentation. They identified the mechanisms by which mutations in the regulatory regions of four genes could affect pigmentation and its variability. They also identified a new gene, CYB561A3, that regulates skin pigmentation. This work expanded the repertoire of genes we know to be involved in the processes driving pigmentation diversity.

By exploring the scientific and genetic underpinnings of skin colour diversity, we gain insights into the biological processes and our shared evolutionary history as well as confront the complexities of social norms, privilege, and prejudice. Embracing diversity prepares us to embrace the rich heritage of humankind and inspires us to strive for more harmonious living.

The authors are senior consultants at the Vishwanath Cancer Care Foundation and adjunct professors at Indian Institute of Technology, Kanpur. All opinions expressed are personal.