The Role of Subtractive Color Mixing in the Perception of Blue Nevi and Veins—Beyond the Tyndall Effect

The original study¹ that proposed the “Tyndall effect” as the explanation behind the coloration of blue nevi drew from spectrophotometric data on cadaveric skin and not the direct study of blue nevi. Since then, the moniker of the Tyndall effect has been applied to a variety of blue phenomena in the skin despite a lack of confirmatory data. We hypothesized that other light-skin optical characteristics may provide a better explanation for the visual phenomenon associated with why blue nevi appear blue.

To briefly review the optics of the skin, perceived color is produced by light that strikes the skin and is remitted (a combination of light reflected and scattered back to the eye). The epidermis plays a minimal role in scattering, responsible primarily for the baseline reflectance of 5% to 7% of light from the skin surface.² The Tyndall effect originally described the preferential scattering of shorter wavelength blue light through particulate matter in air and fluids, and its application to solid tissue optics is based on extrapolative hypotheses. Accordingly, such scattering would occur in a homogenous manner diffusely throughout the skin, not only in blue nevi, which led us to believe that the Tyndall effect does not fully account for the optics associated with blue nevi and veins.