Non‐invasive quantification of melanin in the stratum corneum: a novel indicator of skin lesions in pigmentation diseases

Background/Purpose Skin melanin content is an important indicator for ascertaining the pathology of skin pigmentation diseases, but its analysis necessitates a biopsy or other means of collecting tissue, posing a considerable burden to the patient, and making it difficult to observe how a given skin site changes over time. Here, we aimed to establish a non‐invasive method for quantifying the eumelanin and pheomelanin content of the stratum corneum. Methods Sun‐exposed and non‐exposed samples from 10 healthy Japanese subjects were compared. We harvested the outermost layer of the stratum corneum by tape‐stripping, considering the outer side of the forearm as a sun‐exposed area, and medial side of the upper arm as a non‐exposed area. Four additional subjects were included in the analysis of change in melanin content over time at the same skin site. The anterior lower leg received a single exposure to two minimal erythema dose sunlight, and the stratum corneum was harvested from the same site over a period of 20 weeks; we subsequently quantified the levels of eumelanin and pheomelanin using high‐performance liquid chromatography. Results We were able to accurately quantify the eumelanin and pheomelanin contents of the stratum corneum, and to observe the evolution of the same skin site over time. Eumelanin levels were significantly higher in the sun‐exposed area, with a peak in melanin observed after 11–15 weeks of sun exposure. Conclusion This non‐invasive method can serve as a marker for pathology of skin pigmentation diseases such as malignant tumors.