Diffuse Reflectance Spectroscopy Versus Mexameter(®) MX18 Measurements of Melanin and Erythema in an African Population.

Melanin provides protection against excess exposure to solar ultraviolet radiation (UVR) and related adverse health effects. Diffuse reflectance spectroscopy (DRS) can be used to calculate cutaneous melanin and erythema, but this is complex and has been mostly used for light-to-medium pigmented skin. Handheld reflectance spectrophotometers, such as the Mexameter(®) MX18, can also be used. We compared DRS-calculated melanin and erythema values with Mexameter melanin and erythema index values to understand how these techniques/measurements correlate in an African population of predominantly deeply pigmented skin. Five hundred and three participants comprised 68.5% self-identified Black African, 9.9% Indian/Asian, 18.4% White and 2.9% Colored. The majority of Black African (45%), Indian/Asian (34%) and Colored (53%) participants self-identified their skin as being "brown." Measured melanin levels increased with darker self-reported skin color. DRS-calculated and Mexameter melanin values demonstrated a positive correlation (Spearman rho = 0.87, P < 0.001). The results from both instruments showed erythema values were strongly correlated with their own melanin values. This finding is considered spurious and may result from the complexity of separating brown and red pigment when using narrowband reflectance techniques. Further work is needed to understand melanin, erythema and color in Black skin given sun-related health risks in vulnerable groups in Africa.

Diffuse reflectance spectroscopy as a tool to measure the absorption coefficient in skin: South African skin phototypes.

In any laser skin treatment, the optical properties (absorption and scattering coefficients) are important parameters. The melanin content of skin influences the absorption of light in the skin. The spread in the values of the absorption coefficients for the South African skin phototypes are not known. A diffuse reflectance probe consisting of a ring of six light delivery fibers and a central collecting fiber was used to measure the diffused reflected light from the arms of 30 volunteers with skin phototypes I-V (on the Fitzpatrick scale). The absorption coefficient was calculated from these measurements. This real-time in vivo technique was used to determine the absorption coefficient of sun-exposed and -protected areas on the arm. The range of typical absorption coefficients for the South African skin phototypes is reported. The values for the darker South African skin types were much higher than was previously reported for darker skin phototypes. In the analysis, the contributions of the eumelanin and pheomelanin were separated, which resulted in improved curve fitting for volunteers of southern Asian ethnicity without compromising the other groups.

Modeling and verification of melanin concentration on human skin type.

Lasers are used in the minimalistic or noninvasive diagnosis and treatment of skin disorders. Less laser light reaches the deeper skin layers in dark skin types, due to its higher epidermal melanin concentration compared with lighter skin. Laser-tissue interaction modeling software can correct for this by adapting the dose applied to the skin. This necessitates an easy and reliable method to determine the skin's type. Noninvasive measurement of the skin's melanin content is the best method. However, access to samples of all skin types is often limited and skin-like phantoms are used instead. This study's objective is to compare experimentally measured absorption features of liquid skin-like phantoms representing Skin Types I-VI with a realistic skin computational model component of ASAP(®). Sample UV-VIS transmittance spectra were measured from 370 to 900 nm and compared with simulated results from ASAP(®) using the same optical parameters. Results indicated nonmonotonic absorption features towards shorter wavelengths, which may allow for more accurate ways of determining melanin concentration and expected absorption through the epidermal layer. This suggests possible use in representing optical characteristics of real skin. However, a more comprehensive model and phantoms are necessary to account for the effects of sun exposure.