Insights into Tanning Biology and Tanning Products.
This systematic review, conducted following PRISMA guidelines, synthesizes findings from 68 peer-reviewed studies examining the mechanisms, clinical applications, formulations, and adverse effects of four major sunless tanning agents: dihydroxyacetone (DHA), melanotan (I and II), forskolin, and carotenoids. The authors found that DHA produces skin pigmentation through the Maillard reaction (a non-enzymatic browning of amino acids in the stratum corneum) and has shown additional dermatologic utility in vitiligo and erythropoietic protoporphyria, as well as potential antifungal properties—though concerns about cytotoxicity, genotoxicity, and systemic absorption were noted. Melanotan I and II, which act on melanocortin receptors, were associated with serious adverse effects in unregulated use, including rhabdomyolysis, renal infarction, and priapism. Forskolin was reported to stimulate melanin production independently of melanocortin receptors, with efficacy demonstrated primarily in animal models. Orally ingested carotenoids were found to accumulate in skin and subcutaneous fat, producing a yellow-orange hue. The review acknowledges significant limitations: lack of standardized reporting, heterogeneous outcomes across studies, and insufficient long-term human safety data, particularly for forskolin and carotenoids. The authors conclude that further rigorous clinical research and updated regulatory guidance are needed.