黑色素對於人類皮膚細胞是光照保護劑（Photoprotector）或光照致敏劑（Photosensitizer），長久以來仍存有許多爭議。流行病學的研究顯示：深膚色人種與白種人相較，因紫外線引發皮膚損傷，包括黑色素瘤或其他皮膚腫瘤的機會較少。然而，過去的研究也發現：黑色素及其中間產物與前驅物在接受紫外線照射後會產生反應性氧化物質（reactive-oxygen species），因此顯示黑色素也是有效的光照致敏劑。經過十年來不斷創新與前所未有的研究，使我們更加擴展對黑色素的認知與瞭解。黑色素是由酥胺酸（tyrosine）氧化所形成之單元體所建構之高度不規則異化之聚合物，其包含兩種構型：eumelanin及pheomelanin。目前證實：eumelanin 是具有光照保護效果的色素，而 pheomelanin在紫外線照射後會產生細胞毒性。黑色素與游離輻射也存在有類似的效應：eumelanin 不僅有光照保護效果，同時也有輻射保護效果，這與臨床上所觀察到惡性黑色素瘤細胞之輻射抵抗性的現象相符合。因此若能阻斷 eumelanin 色素的合成過程，對於增進惡性黑色素瘤的放射治療效果當有潛在的意義。

It continues to be debated whether melanins are photoprotecting or photosensitizing in human skin cells. Epidemiologic studies have demonstrated that dark-skinned people are much less susceptible than Caucasians to ultraviolet (UV)-induced skin damage including both non-melanoma and melanoma skin cancer. On the other hand, melanin, its intermediates and precursors can generate reactive-oxygen species when irradiated with UV irradiation and have been shown to be effective photosensitizers. The last decade has witnessed a renewed and unprecedented impetus in melanin research that has significantly expanded our knowledge of this field. Melanin is a highly irregular heteropolymer consisting of monomeric units derived from the enzymatic oxidation of the amino acid tyrosine. There are two distinct types of melanin, eumelanin and pheomelanin. Now, it is proved that eumelanins are the main photoprotective pigment in the epidermis and pheomelanins are phototoxic upon irradiation. The same situation is also true for ionizing radiation that eumelanin not only possesses radiation protective effect but also contains photoprotective ability. Since malignant melanoma is resistant to radiation therapy, therapeutic strategies targeted to the melanogenesis of eumelanin may have potential benefit for the radiation therapy of malignant melanoma.