SUN EXPOSURE AND SKIN RESPONSE MECHANISMS
Too much sun exposure can lead to sunburning which accelerates skin aging and increases the risk of various types of skin cancer [1]. But how does radiation from the sun affect our skin on a daily basis? And what exactly happens when we get sunburnt?
WHAT DOES UV RADIATION DO TO THE SKIN?
When the invisible ultraviolet (UV) rays emitted from the sun hit the skin, DNA is damaged directly by UVB rays and indirectly by the free radicals generated when UVA and UVB rays react with other macromolecules [2]. Accumulation of this damage over time leads to mutations and decreases in the efficiency of cellular waste removal and recycling processes.While it sounds devastating, our cells are equipped with numerous repair mechanisms that reverse DNA damage and signal to melanocytes to boost production of eumelanin, the most common form of melanin. Eumelanin absorbs and dissipates energy from UV rays as heat which stops the generation of damaging free radicals [3]. We can see this in action by looking to epidemiological findings revealing that darker skinned populations have comparatively low skin cancer rates [4].
WHAT IS A SUNBURN?
Too much UV exposure causes high levels of DNA damage to a point that it becomes more energetically favorable for the cell to self-destruct in a process known as apoptosis than to repair the damage. When these cells die, they release inflammatory signals that cause vasodilation of blood vessels, swelling, and inflammation which create the red, puffy look of sunburns [5]. The dead cells are then later shed as new keratinocytes divide and mature up through the epidermis.
UV RADIATION AND SKIN AGING
Spending time in the sun has numerous benefits including increased vitamin D production, melanin production, and immune regulation [6,7]. However, to achieve these benefits, only about 15 minutes of sun exposure 2-3 days/week to the face, arms, and legs is necessary for people with lighter skin tones [8]. Because of the variability in latitude and genetic skin type, dermatologists err on the side of caution and recommend wearing mineral sunscreen on the sensitive facial skin every day.Excessive sun exposure, even without becoming sunburnt, causes oxidative damage that breaks down collagen and impairs collagen synthesis, leading to dehydrated and wrinkled skin [9,10]. Discoloration in the form of solar lentigines, otherwise know as age spots, may also result from dysregulated keratinocyte cell-cell communication which increases with UV exposure [11].We shouldn’t be afraid of sun exposure but erring on the side of caution by utilizing sunscreen to avoid sunburns is critical to maintaining skin health which goes hand in hand with skin appearance.
Sources:
1. Agarwal N (2019) UVR and Role of Pigmentation in Skin Aging and Cancer. InSkin Aging & Cancer: Ambient UV-R Exposure, Dwivedi A, Agarwal N, Ray L, Tripathi AK, eds. Springer, Singapore, pp. 59–69.
2. Lee C-H, Wu S-B, Hong C-H, Yu H-S, Wei Y-H (2013) Molecular Mechanisms of UV-Induced Apoptosis and Its Effects on Skin Residential Cells: The Implication in UV-Based Phototherapy.International Journal of Molecular Sciences 14, 6414–6435.
3. Maddodi N, Jayanthy A, Setaluri V (2012) Shining Light on Skin Pigmentation: The Darker and the Brighter Side of Effects of UV Radiation.Photochem Photobiol 88, 1075–1082.
4. Battie C, Gohara M, Verschoore M, Roberts W (2013) Skin cancer in skin of color: an update on current facts, trends, and misconceptions.J Drugs Dermatol 12, 194–198.
5. Guerra KC, Urban K, Crane JS (2021) Sunburn. InStatPearls StatPearls Publishing, Treasure Island (FL).
6. Kripke ML (2013) Reflections on the field of photoimmunology.J Invest Dermatol 133, 27–30.
7. González Maglio DH, Paz ML, Leoni J (2016) Sunlight Effects on Immune System: Is There Something Else in addition to UV-Induced Immunosuppression?Biomed Res Int 2016, 1934518.
8. Hoel DG, Berwick M, de Gruijl FR, Holick MF (2016) The risks and benefits of sun exposure 2016.Dermatoendocrinol 8, e1248325.
9. Poon F, Kang S, Chien AL (2015) Mechanisms and treatments of photoaging.Photodermatology, Photoimmunology & Photomedicine 31, 65–74.
10. Rittié L, Fisher GJ (2015) Natural and Sun-Induced Aging of Human Skin.Cold Spring Harb Perspect Med 5, a015370.
11. Praetorius C, Sturm RA, Steingrimsson E (2014) Sun-induced freckling: ephelides and solar lentigines.Pigment Cell & Melanoma Research 27, 339–350.