Could Sunglasses Cause Skin Cancer?
While in medical school, it was difficult to reconcile the climbing rates of skin cancer among populations of humans that had been exposed to the sun for millennia. What changed in these populations and why?
The pineal gland is a curious pine cone shaped structure located outside the blood brain barrier. Structurally, this gland is located nearly within the center of the human brain but has the unique ability to convert signals of light to neurohormonal messages that are sent throughout the body. The pathways between the visual cortex and neurohormonal response has been demonstrated.(1)
Sun blocking devices have been used by the Inuit, Roman emperors, and Egyptians using carved bones, polished gemstones, and various shading mechanisms. However, sunglasses in their modern form were not in widespread use until the 1920s when Hollywood actors (2) were photographed with sunglasses thus expanding the market to the masses. Interestingly, the rate of melanoma is inversely related to socioeconomic status, as reported in one review. (3). The researchers were unable to determine which factors resulted in this discrepancy. Perhaps, the inability to afford sunglasses or decreased rate of use resulted in reduced rates of melanoma. Another study performed a decade later echoed these initial results. (4) How and why could that occur?
Clock genes respond to external stimuli in the hypothalamus in an area noted in the image above called the superchiasmatic nucleus. These internal timekeepers responds to light (multiple wavelengths) input through elaborating mRNA in nearly every body tissue to create proteins that respond to the stimuli as well as upregulate or downregulate melatonin synthesis and secretion. Clock gene proteins have also been demonstrated in the pineal gland. Furthermore, melatonin may antagonize alpha melanocyte stimulating hormone enhancement of melanogenesis through inhibiting the synthesis of tyrosinase. Tyrosinase is a key factor in the production of melanin (skin pigmentation).
Perhaps, increased blockage of UV radiation to photoreceptors by wearing sunglasses aberrantly alters melatonin secretion creating a signal miscommunication between melanocyte photosensory systems in the skin and signals interpreted by the pineal gland from light stimulation. In essence, the pineal gland misinterprets ambient light conditions and responds accordingly which reduces the capacity for the skin to respond appropriately. Socioeconomic and chronological discrepancies in disease prevalence and incidence associated with the use of sunglasses may further support this theory.
1. Stehle, Jörg H., et al. "A survey of molecular details in the human pineal gland in the light of phylogeny, structure, function and chronobiological diseases." Journal of pineal research 51.1 (2011): 17-43.
3. Harrison, Renée A., et al. "Socioeconomic characteristics and melanoma incidence." Annals of epidemiology 8.5 (1998): 327-333.
4. Clarke, Christina A., et al. "Interaction of area-level socioeconomic status and UV radiation on melanoma occurrence in California." Cancer Epidemiology and Prevention Biomarkers 19.11 (2010): 2727-2733.
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