Abstract
Objective: Humans are increasingly exposed to artificial light and electromagnetic wave radiation, in addition to solar radiation. Many studies have shown the biological effects of ultra-violet and near-infrared exposure, but few have extensively investigated the innate biological defenses within human tissues against visible light and near-infrared exposure. Herein, we investigated spectral properties of endogenous human biological defenses against ultra-violet to near-infrared. Methods: A double-beam spectrophotometer (190 - 2700 nm) was used to measure the transmission spectra of a saline solution used to imitate perspiration, and oil to imitate sebum, as well as human skin, blood, adipose tissue, and muscle. Results: Saline (thickness, 0.5 mm) blocked 27.5% - 98.6% of ultra-violet, 13.2% - 34.3% of visible light, and 10.7% - 99.8% of near-infrared. Oil (thickness, 0.5 mm) blocked 50.5% - 100% of ultra-violet, 28.7% - 54.8% of visible light, and 19.0% - 98.3% of near-infrared. Blood thicknesses of 0.05 and 0.5 mm blocked over 97.8%, 100% of ultra-violet, over 94.6%, 99.7% of visible light, and over 75.8%, 99.4% of near-infrared, respectively. Skin thicknesses of 0.25 and 0.5 mm blocked over 99.4%, 100% of ultra-violet and over 94.3%, 99.7% of visible light, and over 74.7%, 93.5% of near-infrared, respectively. Adipose tissue thickness of 0.25 and0.5 mm blocked over 98.3%, 100% of ultra-violet, over 94.7%, 99.7% of visible light, and over 88.1%, 98.6% of near-infrared, respectively. Muscle thickness of 0.25 and0.5 mm blocked over 95.4%, 99.8% of ultra-violet, over 93.1%, 99.5% of visible light, and over 86.9%, 98.3% of near-infrared, respectively. Conclusions: Humans possess endogenous biological protection against ultra-violet, visible light and near-infrared exposure on multiple levels, including through perspiration, sebum, blood, skin, adipose tissue, and muscle. Since solar and artificial radiation affects human tissues, biological defenses made of biological materials may be induced to protect subcutaneous tissues against these wavelengths.
Highlights
Incident solar energy is composed of 6.8% ultra-violet (UV), 38.9% visible light (Vis), and 54.3% near-infrared (NIR) [1]
When life first originated on Earth, the first life forms appeared in water and they did not need to adapt to dehydration, gravity, or sunlight including UV, Vis, and NIR as the surrounding water served as a barrier against these obstacles [2]
Insects can remain in sunny environments without much perspiration because they consist of fibrous chitin and alpha helical proteins that efficiently block and absorb NIR, thereby preventing their body temperature from becoming elevated
Summary
Incident solar energy is composed of 6.8% ultra-violet (UV), 38.9% visible light (Vis), and 54.3% near-infrared (NIR) [1]. The fibrous structural proteins rich in hydrogen bonds and alpha helices are useful for blocking NIR because they efficiently absorb these wavelengths [2]. Insects can remain in sunny environments without much perspiration because they consist of fibrous chitin and alpha helical proteins that efficiently block and absorb NIR, thereby preventing their body temperature from becoming elevated. Sheep prefer the sun to the shade, and even though these animals remain in sunny environments without much perspiration, their body temperature does not become elevated as sheep wool consists of alpha helical structures [2]. Humans possess endogenous protective mechanisms against UV, Vis, and NIR exposure on multiple levels, including perspiration, blisters, sebum, hair, melanin, vasodilation, skin, and adipose tissue, in addition to protective materials such as cotton or wool clothing [2]. Many studies have shown the defensive capabilities of human tissues against UV exposure, their ability to protect against Vis and NIR exposure has not been thoroughly investigated
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