Updated: Jul 7, 2020
Solar is the source of energy to the Earth, it warms the Earth, causes weather change, and sustains plant and animal life.
However, it gives our skin hard times.
We all know about fighting against the UVA and UVB light rays when it comes to skin protection from the sun exposure. However, in addition to UV, a broader spectrum of solar radiation has been researched and is found to contribute to pre-mature aging, i.e. photo-aging. This will accelerate the appearance of wrinkles, age spots and discoloration. Skin will also lose its firmness and elasticity.
Here is a summary of how each light ray causes damage to our skin.
Appropriate percentage of solar radiation reaching the earth
Accounting for less than 1% of solar radiation reaching the earth, UVB exposure is mainly at outdoor as it can be filtered by glass. In HK, UV rays are at their strongest at 11am to 4pm during the day, and between July and October every year. UVB rays can penetrate to the basal cells of the epidermis, cause reddening and sunburn of the skin, and damage DNA in skin cells directly.
UVA rays are the major cause of premature skin-aging and tanning. It is less dependent on the time of the day and is prevalent in all kind of weather or season. UVA rays can penetrate clouds and glass, so we are still exposed to it at indoor. Tanning bed is also a source of UVA. With longer wavelength, UVA rays penetrate into the dermis and produce free radicals, i.e. reactive oxygen species (ROS), which cause inflammation and DNA damage. It also cause hyperpigmentation and lead to wrinkles and other signs of aging by breaking down of healthy collagen and elastin.
Blue light is the high-energy visible (HEV) light with wavelength of 400-450 nm (nanometer). Sun exposure, LED from indoor lighting and digital devices are the major sources. Exposure to blue light has been claimed to have similar impact on the skin damage as the UVA rays.
Research on how blue light affects the skin is still ongoing and it is still yet to be conclusive. However, studies have shown that blue light from electronic devices, to which we expose more often than ever, can increase the generation of ROS. Research showed that ROS in human fibroblasts increased significantly even after short exposure to blue light. HEV also causes long-lasting skin pigmentation. Blue light also delay skin barrier recovery after disruption.
It is the sub-category of IR - near infrared (IRA) with wavelength of 740 to 1400 nm - that we should be concerned of as more than 65% of IRA reaches the dermis. Sunscreens neither filter nor reflect IR radiations. Unlike UV which generates ROS directly in cell membrane, studies show that IRA induces their formation in mitochondria. The damages it induces, not just destruction of collagen and reduction in collagen synthesis, but also the impact on mitochondria’s energy production for biological process, affect the entire cell and tissue.
Source: Hong Kong Cancer Fund, Skin Cancer Foundation, Institute of Personal Care Science, Mibelle Group, NCBI