The Use of Spectrophotometry to Estimate Melanin Density in

The density of cutaneous melanin may be the property of the skin that protects it from damage by solar radiation, but there is not an accepted, noninvasive method of measuring it. To determine whether the density of cutaneous melanin can be estimated from reflectance of visible light by the skin, reflectance of 15-nm wavebands of light by the skin of the inner upper arm of each of 82 volunteers was measured at 20-nm intervals with a Minolta 508 spectrophotometer. A 3-mm skin biopsy was then taken from the same site, and four nonserial sections of it were stained with Masson Fontana for melanin. The melanin content of the basal area was calculated using the NIH Image analysis system. We show that cutaneous melanin in Caucasians can be estimated by the difference between two measurements of reflectance of visible light by the skin: those at wavelengths 400 and 420 nm. This new spectrophotometric measurement was more highly correlated (r = 0.68) with the histological measurements of cutaneous melanin than was skin reflectance of light of wavelength 680 nm (r 0.33). Reflectances in the range of 650-700 nm have been used previously in skin cancer research. This relatively accurate measurement of melanin is quick and nomnvasive and can be readily used in the field. It should provide improved discrimination of individual susceptibility to epidermal tumors in Caucasians and information about melanin’s biological role in the causation of skin cancer. Introduction Researchers in several fields have been interested in estimating the concentration and type of melanin in tissues of epidermal origin, including the skin, hair, and iris. For anthropologists, the interest has been in tracing the geographic and cultural origins of individuals and populations (1). In medicine, this interest has Received 7/29/97; revised 12/9/97; accepted 12/18/97. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 This research was supported by the National Health & Medical Research Council of Australia. 2 To whom requests for reprints should be addressed, at Menzies Centre for Population Health Research, 17 Liverpool Street, Hobart, Tasmania 7000. Australia. Phone: 61-3-6226-7700; Fax: 61-3-6226-7704; E-mail: [email protected]. principally stemmed from the desire to determine susceptibility to epidermal tumors (2). The risk of melanoma is determined by sun exposure and by skin phenotype. The observation of differences in risk of melanoma between racial groups, with Caucasians having a much higher incidence of melanoma than Africans or Asians, strongly supports this inference about the role of skin phenotype. It also seems probable that, among Caucasians, risk of both melanoma and other skin tumors differs by skin phenotype. Measurable properties that could reasonably be thought to be related to or to characterize skin phenotype include eye color, hair color, and skin color. Those properties have been used as indicators of skin phenotype because they appear to be clear markers of the type of biological difference that distinguishes Caucasians from lower-risk populations. Although the basis for the choice of measurements has not usually been made explicit, it is likely that they have been used as proxies for melanin density or melanin type in the skin. There have been attempts to estimate melanin density in the skin using reflectometers. As early as 1939, Edwards and Duntley (3) demonstrated that the reflectance of light in the visible spectrum (400-700 nm) is influenced by the presence of melanin, as well as by hemoglobin and carotene. Melanin was found to absorb more light at shorter wavelengths and to exhibit steadily decreasing absorption up to 700 nm. Absorptions by hemoglobin and by carotene were more intermittent, with peaks at 418-429 nm and 542-576 nm (hemoglobin) and at 482 nm (carotene). The subsequent development of noninvasive skin reflectance measurements of melanin density focused on reflectance at wavelengths of 650-700 nm in the belief (4) that, although absorption by melanin at those wavelengths was relatively low, the total absorption of light could be attributed solely to the presence of melanin because there was no contribution by hemoglobin or carotene. The extent to which melanin is truly estimated by reflectance at those wavelengths or any other has not been previously assessed by direct comparison with actual melanm density in the skin. Here, we compared the epidermal concentration of melanin, analyzed histologically in skin biopsy specimens, with skin reflectance, measured by a spectrophotometer, to find the best reflectance estimate of melanin density. The skin biopsy and the spectrophotometric measurement for each subject were obtained from a site on the inner upper arm, an area not usually exposed to the sun. This site was defined as the midpoint of a line drawn from the epicondyle of the humerus to the point where the axilla joins the upper chest. We also examined the correlation of the commonly used proxies for skin phenotype, eye, hair color, and self-perceived skin type with the direct measurement of cutaneous melanin density. on November 6, 2017. © 1998 American Association for Cancer Research. cebp.aacrjournals.org Downloaded from