Skin Pigment and Medical Device Performance

Skin Pigment Impact on Medical Device Efficacy
Skin Pigment Impact on Medical Device Efficacy. Source: US FDA.

A recent 2023 study from the US FDA is titled “Impact of Skin Pigmentation on The Performance of Biomedical Optics Devices.” It is very interesting and the above poster image has very precise details spelled out. Make sure to also read my recent post on the lack of representation of darker skin in medical texts in the US and Western Europe.

Skin Pigment and Biomedical Device Performance

Melanin is recognized to be a major absorber of light in the skin. While melanin is the main factor in determining skin color, it can also significantly impact signals detected by optical medical devices. The authors of this latest study break out the biomedical devices analyzed into six categories:

  1. Cerebral/Tissue oximeters (675-950 nm wavelength).
  2. Hyperspectral imaging systems (400-1,000 nm).
  3. Photoacoustic imagers (550-900 nm).
  4. Wearables/PPGs (450-900 nm).
  5. Transcutaneous bilirubinometers (380-760 nm).
  6. Raman spectroscopy devices (550-1,100 nm).

In all six medical device types, the level of skin pigment in a patient makes a difference in how well each device works. What the authors call a skin pigmentation bias. The offer suggestions on mitigation procedure for all technologies other than for wearables/PPG (photoplethysmography).

Impact of Pigmentation and Solutions

Among the problems associated with increased skin pigment include:

  • Reduced signals at shorter wavelengths.
  • Intensity reduction.
  • Reduced waveform modulation and amplitude.
  • Excess device light absorption by the melanin in the skin.
  • Undesired spectral shifts.
  • Strong pressure transients in the epidermis, increasing near-surface clutter and noise.
  • Lower signal to noise ratio in the dermis.
  • Alteration in blood oxygenation estimates.
  • Melanin has the potential to absorb both excitation light and Raman scattering.

Among the various mitigation measures that are suggested include: stronger light sources; higher detector sensitivity; narrower probe spacing; multiple source-detector separation distances and processing algorithms; weighted subtractions in hyperspectral reflectance imaging (HRI) devices; multiple wavelength utilization; fluence correction algorithms to compensate for spectral coloring; revision of illumination detection design; and numerical background correction approaches.

In recent years, clinical studies of pulse oximetry have garnered much attention in finding evidence of racial disparities in performance. This latest research indicates that other biomedical optics technologies can also be affected significantly by skin pigmentation levels in people of color.

Optical characteristics of skin melanin including absorption, scattering and fluorescence. There needs to be increased awareness by medical professionals in regards to the mechanisms and effects of epidermal melanin on detected optical signals. Feedback can help device manufacturers improve their technology. Moreover, government regulatory staff can then institute appropriate practices to avoid racial disparities in medical device efficacy.

Common Skin Problems in People with Dark Skin

Skin Conditions in People of Color.
Skin Conditions in People of Color.

Common skin problems for people with darker skin tones

People with dark skin may experience a range of skin issues that are unique due to their higher levels of melanin. It is important to note that while skin conditions affect people of all skin tones, certain concerns may be more noticeable or present themselves differently in those with darker skin. Below are some common skin problems in people with dark skin:

  • Hyperpigmentation: This is the most common of all the skin problems that afflict people of color. Darker skin is more prone to hyperpigmentation, which can result from conditions such as acne, eczema, or injury. Dark spots or patches may develop be more persistent and noticeable.
  • Keloids: Darker skin has a higher tendency to form keloids, which are raised overgrowths of scar tissue. Keloids can develop after minor injuries or surgical procedures and may be more prominent in individuals with darker skin tones.
  • Post-inflammatory Hyperpigmentation (PIH): PIH occurs after skin inflammation or injury, leaving behind dark spots or discoloration. Darker skin tones are more susceptible to PIH, and the pigmentation changes can last longer.
  • Acne: Acne can affect individuals of any skin tone, but the aftermath (such as hyperpigmentation or keloid scarring) may be more noticeable in people with darker skin.
  • Acanthosis Nigricans: This condition is characterized by dark, thickened, velvety patches of skin, often around the neck, armpits, or other body folds. It is associated with insulin resistance and obesity. According to the American Academy of Dermatology (AAD). Acanthosis nigricans can also be an early warning sign of diabetes, hormonal problems such as PCOS and even skin cancer.
  • Hypopigmentation Disorders: In addition to hyperpigmentation, disorders leading to loss of skin color (such as vitiligo) may be more visually striking in individuals with darker skin.
  • Rosacea: Easy to miss in people with darker skin. In lighter skinned people, it causes redness. In people of color, the affected skin can often appear darker and brown in color.
  • Ashy Dermatosis: This skin problem is more common in individuals with darker skin. It leads to gray or ashy patches on the skin, usually on the legs.
  • Pseudofolliculitis Barbae (Razor Bumps): Due to the curly nature of hair in people with dark skin, shaving can sometimes lead to ingrown hairs, resulting in razor bumps and inflammation.
  • Eczema (Atopic Dermatitis): Eczema can affect individuals of all skin tones, but it might be more noticeable in dark skin due to hyperpigmentation or hypopigmentation associated with the condition. The skin may appear ashy, and scratching can lead to post-inflammatory hyperpigmentation.
  • Psoriasis: Psoriasis can manifest differently in people with darker skin. The plaques may be darker or more pigmented, making them easily mistaken for other skin conditions.
  • Dermatosis Papulosa Nigra: This condition is characterized by small, dark bumps, often seen on the face, neck, or chest. It is more common in individuals with darker skin.
  • Lichen Planus: Dark skin may exhibit hyperpigmented or hypopigmented patches due to lichen planus, an inflammatory skin condition.
  • Tinea (Fungal Infections): Fungal infections, such as tinea versicolor, can cause changes in skin pigmentation. In darker skin, these infections may result in hypopigmented or hyperpigmented patches.
  • Seborrheic Dermatitis: This chronic inflammatory condition can affect the scalp, face, and other areas, leading to redness, scaling, and sometimes hyperpigmentation, particularly in individuals with darker skin.
  • Folliculitis: Inflammation of hair follicles can result in dark spots or keloid scars in people with dark skin, especially if the condition becomes chronic.
  • Moles and Melanoma: While people with darker skin are less prone to developing melanoma, when it occurs, it is often diagnosed at a later, more advanced stage. It’s essential for individuals with dark skin to regularly check for changes in moles and seek prompt medical attention if any are noticed.
  • Allergic Contact Dermatitis: Pigmented skin may respond to allergens or irritants with hyperpigmentation or hypopigmentation, creating distinctive patterns on the skin.
  • Granuloma Annulare: This chronic skin condition can cause raised, reddish or skin-colored bumps in a ring pattern. In individuals with dark skin, the lesions may appear hyperpigmented.
  • Xerosis (Dry Skin): People of color may be more prone to dryness. This leads to conditions like xerosis, which can cause itchiness, scaling, and discomfort.
  • Hidradenitis Suppurativa: This chronic skin condition involves the inflammation of hair follicles, resulting in painful nodules, lumps and abscesses. In people with dark skin, scarring and hyperpigmentation may be more prominent.

It’s important for individuals with dark skin problems to seek dermatological care from professionals who understand the unique challenges and characteristics of darker skin tones. Early diagnosis and appropriate management can help address these skin concerns effectively. Additionally, proper skincare practices, including sun protection, can contribute to maintaining healthy skin in individuals of all skin tones.

Skin Problems in Dark Skin.
Skin Problems in Dark Skin.

Darker Skin Absent from Medical Texts

According to a recent paper, people with black and brown skin tones are underrepresented in medical textbooks that teach doctors on how to recognize skin disease. The shortfall in darker skin representation could contribute to racial disparities in diagnosis and treatment. The research was conducted via the use of machine learning and AI.

Darker Skin Segmentation
Darker Skin Segmentation and Pixels. Source: Tadesse, G.A., Cintas, C., Varshney, K.R. et al. Skin Tone Analysis for Representation in Educational Materials (STAR-ED) using Machine Learning.

Skin Tone Analysis for Representation in Educational Materials

The original paper was published in August 2023 and included reserchers from the US and Kenya. It is titled: “Skin Tone Analysis for Representation in Educational Materials (STAR-ED) using machine learning”. They analyzed skin-related pixels and non-skin related pixels and made comparisons using the Jaccard index. STAR-ED works on a wide range of file formats, including pdf, png, jpeg, pptx and docx.

One of the lead authors is Dr. Roxana Daneshjou, a dermatologist and biomedical data scientist from Stanford University. In her words:

Unfairness in the teaching materials equates to unfairness in society.

There’s lots of news out there of bias in AI models, but in this case we’ve trained an AI model that detects human bias.

STAR-ED is open source. Both the code and dataset are available for download via GitHub.

Underrepresentation of Darker Skin Tones

The research team trained STAR-ED on thousands of images in medical textbooks, lecture notes, presentation slides, and journal articles. They found that only one in ten images throughout these materials is in the black-brown range on the Fitzpatrick Scale used to evaluate skin tone.

The researchers envision this unique STAR-ED technology to be used as a tool for dermatology educators and publishers. It will help assess educational materials and automatically identify and significant lack of diverse skin tone representation.

Besides the technology’s use for various cosmetic concerns, there is an even bigger issue at play. At present, the diagnosis of life threatening conditions such as skin cancer (melanoma and squamous cell carcinoma) is often delayed in patients of color, leading to increased mortality rates.

Some dermatologists are taking the matter into their own hands. Dr. Jenna Lester started the Skin of Color Program at the University of California, San Francisco in 2018. She wanted to train dermatology residents in treating skin of color. Skin conditions such as eczema, psoriasis, inflammation, acne and hyperpigmentation show up differently in people of different colors and ethnicities.