Sunlight is composed of electromagnetic waves, which include ultraviolet (UV) radiation, visible light, and infrared radiation (IR). The UV radiation emitted from the sun can be divided into 3 types according to wavelength: UVA (315-400 nm), UVB (280-315 nm), and UVC (100-280 nm). Due to absorption by the Earth's atmospheric layers, UVC radiation cannot penetrate through to reach the Earth's surface. UVA and UVB rays are able to pass through the earth's atmosphere and reach the surface. Typically, the UV radiation reaching the earth's surface is composed of around 90-95% of UVA and 5-10% of UVB.

          UV radiation can penetrate the human skin layer. This has both benefits and harms to human skin. When exposed to an appropriate amount of UVC radiation, the body undergoes increased synthesis of Vitamin D3 within the skin, promoting bone strength and muscle function. However, excessive exposure may lead to adverse effects on the body's skin.

         UVA rays can penetrate deeper into the dermis layer, while the shorter wavelength UVB rays only reach the epidermis layer. Both types of UV radiation affect the DNA molecules in skin cells. UVA rays can stimulate the production of reactive oxygen species (ROS) within cells, inhibiting cells' self-repair capabilities. UVA also causes DNA adducts which can lead to mutations and the development of cancer cells, and induces inflammatory responses that damage skin cells. UVB rays cause DNA structural rearrangements like cyclobutane pyrimidine dimers (CPDs) or 6-4 pyrimidine pyrimidone photoproducts (6-4PPs), creating covalent bonds between DNA bases that prevent the DNA from functioning properly. UVB also generates reactive oxygen species, causing DNA mutations and suppressing immune cells, potentially leading to cell death or cancer cells.

Dangers of UV Radiation To The Skin

          Sunlight containing UV rays can damage DNA, cause inflammation, and induce cell mutation. Prolonged sun exposure may lead to the following effects on the skin

• Wrinkles

         Wrinkles can arise from cellular aging and prolonged sun exposure. UV exposure generates reactive oxygen species that stimulate collagen breakdown by increasing matrix metalloproteinases (MMPs), which cleave collagen fibers, while also reducing new collagen production. This leads to a loss of skin firmness and elasticity, causing wrinkles.

• Melasma, Freckles, and Dark Spots

         These conditions involve areas of hyperpigmentation of the skin due to increased melanin production by melanocyte cells. UV exposure generates reactive oxygen species that stimulate the nitric oxide (NO) pathway in melanocytes, boosting melanin production and darkening the skin.

• Sunburn

         Prolonged UVB exposure can cause sunburn by inducing the release of cytokines and other inflammatory mediators, leading to redness, stinging, and irritation.

• Skin Cancer

         UV radiation has the capability to directly harm DNA by forming bonds between its bases, produce reactive oxygen species (ROS) that harm both DNA and cellular structures, and hinder immune cells responsible for eliminating cancer cells. Failure to adequately repair this DNA damage may result in mutations, potentially paving the way for the development of cancer.

[References]

1. -, T. S., & -, D. S. (2023, May 19). Current Understanding of the Effects of Sun Exposure on Skin Tanning: Mechanisms, Risks, and Protective Strategies. International Journal for Multidisciplinary Research, 5(3). https://doi.org/10.36948/ijfmr.2023.v05i03.3115

2. Halliday, G. M., Norval, M., Byrne, S. N., Huang, X. X., & Wolf, P. (2008, June). The effects of sunlight on the skin. Drug Discovery Today: Disease Mechanisms, 5(2), e201–e209. https://doi.org/10.1016/j.ddmec.2008.04.005

3. Chaudhary, M., Khan, A., & Gupta, M. (2020, April 25). Skin Ageing: Pathophysiology and Current Market Treatment Approaches. Current Aging Science, 13(1), 22–30. https://doi.org/10.2174/1567205016666190809161115

4. Shin, J. W., Kwon, S. H., Choi, J. Y., Na, J. I., Huh, C. H., Choi, H. R., & Park, K. C. (2019, April 29). Molecular Mechanisms of Dermal Aging and Antiaging Approaches. International Journal of Molecular Sciences, 20(9), 2126. https://doi.org/10.3390/ijms20092126

5. Ogbechie-Godec, O. A., & Elbuluk, N. (2017, July 19). Melasma: an Up-to-Date Comprehensive Review. Dermatology and Therapy, 7(3), 305–318. https://doi.org/10.1007/s13555-017-0194-1

6. Thawabteh, A. M., Jibreen, A., Karaman, D., Thawabteh, A., & Karaman, R. (2023, June 18). Skin Pigmentation Types, Causes and Treatment—A Review. Molecules, 28(12), 4839. https://doi.org/10.3390/molecules28124839

7. Sun and Skin. (2020, January 6). NIH News in Health. https://newsinhealth.nih.gov/2014/07/sun-skin

8. C. (2023, September 14). Ultraviolet radiation – harmful or harmless? Cordlife Singapore. https://eyescreen.cordlifetech.com/sg/ultraviolet-radiation-harmful-or-harmless

9. Dalal, U. (2023, September 16). Difference Between UVA And UVB Rays. https://www.bebeautiful.in/all-things-skin/everyday/difference-between-uva-and-uvb-rays

10. Volatier, T., Schumacher, B., Cursiefen, C., & Notara, M. (2022, February 10). UV Protection in the Cornea: Failure and Rescue. Biology, 11(2), 278. https://doi.org/10.3390/biology11020278