A study in Photodermatology, Photoimmunology & Photomedicine has uncovered a fascinating link between sun exposure to the eyes and skin pigmentation on other parts of the body. The research demonstrates that UVB radiation hitting the eyes alone can trigger melanocyte activation (the process that darkens skin), but also shows that this effect can be suppressed by the skin-whitening agent, tranexamic acid.
It is well-known that direct UVB exposure on the skin causes tanning and pigmentation. This study explored a less obvious, systemic pathway: can UVB light entering the eyes cause skin to darken elsewhere? The researchers investigated this phenomenon and the mechanism by which tranexamic acid, an amino acid used in skincare, counteracts it.
Key Findings from the Study:
The study used mice to model the effects of localized UVB exposure on the body's pigmentation response.
Eye Exposure Triggers Distant Skin Darkening: When mice had only their eyes exposed to UVB light, they showed a significant increase in the number of activated melanocytes in their ear skin, similar to the effect of directly irradiating the ear.
A Hormone-Driven Mechanism: This pigmentation was driven by a hormonal signal originating from the pituitary gland. UVB eye exposure caused a spike in plasma levels of α-melanocyte-stimulating hormone (α-MSH), the primary hormone that tells skin cells to produce melanin.
Tranexamic Acid Blocks the Signal: Oral administration of tranexamic acid before UVB exposure successfully suppressed both the increase in skin melanocytes and the surge in plasma α-MSH.
Targeting the Source: The study identified the specific enzyme responsible. UVB eye irradiation increased the expression of prohormone convertase 2 (PC2) in the pituitary gland. PC2 is the enzyme that cleaves a precursor molecule (POMC) to create active α-MSH. Tranexamic acid treatment prevented this increase in PC2.
Conclusion:
This research reveals that even indirect sun exposure via the eyes can stimulate a hormonal cascade that leads to skin pigmentation. Tranexamic acid works as a whitening agent in this context by intervening at the source: it suppresses the production of the key enzyme (PC2) in the pituitary gland, thereby preventing the release of the skin-darkening hormone α-MSH.
Source & Link to Original Article:
For credibility and academic integrity, the original research paper is cited below. You can access the full article via the following link.
Citation: Hiramoto, K., Yamate, Y., Sugiyama, D., Takahashi, Y., & Mafune, E. (2014). Tranexamic acid suppresses ultraviolet B eye irradiation-induced melanocyte activation by decreasing the levels of prohormone convertase 2 and alpha-melanocyte-stimulating hormone. Photodermatology, Photoimmunology & Photomedicine, 30(6), 302–307.
Link: https://onlinelibrary.wiley.com/doi/10.1111/phpp.12131
