Blue Spectrum Light & The Skin
All terrestrial life on earth evolved under the pervasive influence of diurnal cycles of varying lengths. These cycles forged many of the mechanisms of life, most familiarly the sleep wake cycle. Depending on latitude and other factors including altitude, the spectrum of light that almost all life on earth interacted with, consisted entirely of solar frequencies (except for the infrared emitted essentially out of all matter, biophotons and fire). These frequencies would change season to season and throughout the course of each day. Both single and multi-celled organisms evolved in this constant flux to anchor their metabolic processes and maximise their productivity and fitness. Consequently, our bodies are exquisitely sensitive to the cycles of light (as well as magnetism) at all levels of our physiology. A salient example of this phenomenon is the drastic impairment of blood glucose regulation when exposed to artificial light (primarily in the blue spectrum) at biologically incongruent times . This is a simple but effective example to highlight how intrinsically linked our biology is to light cycles. Unfortunately, in the modern world, the vast majority of humans are living under artificial lights. To make matters worse, the lighting that the western world has decided to use is lit almost entirely in the blue spectrum (as a side note, this is done because blue frequencies require less power as their frequency lengths are shorter and create little to no heat). Much of the focus surrounding artificial light has been placed around its impact on human physiology and metabolism through the retina. While this research is absolutely not misplaced and probably one of the most important areas of research right now, the impact of these non-native frequencies on out most exposed organ, the skin, has not been touched on nearly as much.
Our skin is the largest direct interface with solar radiation. It is a primary site for immune defence in both direct and indirect ways. More saliently, it acts as a physical barrier, protecting our blood and organs from bacteria and other particulate matter. This is seen in individuals with skin barrier dysfunction where their susceptibility to infections such as Staphylococcus aureus is increased . The skin also play an indirect role in modulating immunity via the synthesis of compounds such as pre-vitamin D through UVB exposure. This point alone demands attention as far as skin physiology and circadian regulation goes; like other organs in the body, the skin uses diurnal cycles to modulate its anabolic phase (build up) and catabolic phase (break down). This can be seen in the expression of DNA repair mechanisms after UV exposure peaking at night . Circadian rhythms of the skin also seem to regulate skin hydration and elasticity via the regulatory actions of clock genes within the skin cells .
Literature reviews on the circadian rhythm of the skin point to key genes including Aquaporin 3 (AQP3) which regulate skin water loss, pH, blood flow, blood temperature, and keratinocyte (skin cell) proliferation being orchestrated by peripheral clocks in the keratinocytes themselves . Clock genes such as Per1, Cry1 and Bmal1 orchestrate the rhythmic molecular functions in all mammalian cells . These clock genes act as transcription factors and influence the activities of the cells, dependant on the environmental exposures . Whilst these clock genes are associated with the master clock in the brain, the suprachiasmatic nucleus (SCN), they are somewhat independent and show a capacity to be altered without altering the SCN, allowing their impact on cell function to be affected independent of light through the eyes . This may be connected with the fact that sleep can be disrupted quite dramatically when light is shone on the back of one’s knee as they are asleep . Essentially the point here is that cells of peripheral tissues such as skin are conducted by timing cues from both the SCN and less universal operations run by these peripheral clock genes. Examining the expression of these tissue specific genes such as per1 can lend insight into the effects of environmental influences on cellular metabolism. Here it is critical to consider skin exposure to artificial lights and the specific time of day.
UV light is considered dangerous by most people today. It has been demonised critically by the dermatology community and has become the focussed attention of governing bodies as they continue to roll out campaigns condemning UV exposure of all forms. While UV light has the potential to cause harm in humans in the wrong context (like all animal studies looking at UV induced mutagenesis), many don’t consider that the frequency that comes right after UV is the visible violet/blue spectrum. I have not heard of anyone ever remark about the potential detrimental effects of these frequencies on the skin, even though they are really only separated by a somewhat arbitrary condition of our capacity to see them. This is a problem that I feel is not addressed enough when considering the health of skin; particularly in discussions surrounding skin cancer. There are, however, studies that are beginning to emerge that look at the nature of these blue light insults on the skin and present compelling data that outlines the first layer of discoveries in this particular field. A paper published last year in a cosmetic science journal highlights some of the points I’ve been trying to make here. In the study, researchers from cosmetic brand Estèe Lauder looked at the impact of blue (410nm) light on human keratinocytes (skin cells) . They focused on the expression of the clock gene per1 as a marker of dysregulation resulting from the exposure of blue light. The group reported several findings including “an increase of ROS production, DNA damage and inflammatory mediators”. This is somewhat worrying in and of itself. However, with the marked down regulation of circadian clock genes such as per1, the repair and recovery from this damage may be the most concerning element. We encounter reactive oxygen species (ROS) and DNA damage constantly, they are as much a part of our normal physiology as is the flow of blood through our veins and arteries. Where we encounter problems is when we impede or damage our innate repair mechanisms that have co-evolved with these insults to keep the balance of damage and repair. What I believe this study demonstrates is that blue light on the skin not only damages our skin, but interrupts the clock genes that regulate skin rejuvenation. It is known that skin growth and repair is a highly circadian process .
“over a 24‐hr natural cycle, during the day, the skin is focused on protection; while at night, the skin is focused on repairing damage that occurred during daytime” 
If care is not taken to cover the skin after any damage, whether it is from UV or blue light, our skin’s circadian rhythmicity may be negatively altered, leading to permanent skin damage. The researchers of this study also used the light of an iPad on the cells to assess the damage in a more appropriate context. Similar results were found in that ROS production rose by 88%, DNA damage increased and per1 activity was diminished. This is telling, as it is the exact type of light most people are exposed to each and every night when their skin should be receiving the signal of darkness. I will point out that I absolutely recognise the limiting nature of the study as it is performed in vitro. I am usually the first to examine these with a very discerning eye when it comes to types of light exposures. However, I am always much more sceptical when cells are exposed to stimulated sunshine as these are very poor representations of the real-world exposures we encounter. In this case, the type of light used is exactly right in the sense that it’s a 1:1 comparison with the light that we are too often exposed to. For this reason I believe it likely resembles some of the changes that occur in our skin cells when we are exposed to artificial lights at night, even though the skin cells are separated from the larger physiology of the body.
I believe that this desynchronisation event that occurs in the skin can play a role in skin damage and possibly non-melanoma skin cancers. This may be particularly true in individuals with low melanin content, vitamin D levels and other protective photoproducts that can quash the damage caused by lower frequency light . Think of the scenario where an individual may spend a whole day at the beach accumulating UV related damage and immune suppression that can be offset by the effects of melatonin and vitamin D , but then they spend at least a few of the dark hours of the night under artificial lighting. This is where altered circadian functioning at the cell level might affect the recovery of the insult accrued that day.
To surmise, the artificial lights that have become ubiquitous today are lit primarily in the blue (400-450nm). These frequencies lie right next to ultraviolet in the colour spectrum and exert profound effects on skin directly and through circadian cues. This circadian incongruence may have notable and accumulating detrimental effects on the skin.