What Can Solar Radiation Do To You?
Solar radiation refers to the radiant energy emitted by the sun in the form of electromagnetic waves. It consists primarily of ultraviolet radiation (UV), visible light, and infrared radiation. Solar radiation is the energy source that allows life to exist on Earth (1). However, overexposure to solar radiation can be harmful to human health. It can lead to consequences such as sunburn, premature skin aging, skin cancer, eye damage and suppression of the immune system (2). This article will provide an overview of the different types of solar radiation and their effects on human health. It will also discuss ways to protect yourself against the potential dangers of overexposure.
UVA Radiation
UVA rays have the longest wavelength and lowest energy of the three types of UV rays. However, UVA rays penetrate deep into the dermis layer of the skin and account for up to 95% of the UV radiation that reaches the Earth’s surface (Amaro-Ortiz, 2014). Although they do not cause sunburn, UVA rays contribute to skin aging and wrinkling. Research shows that repeated exposure to UVA radiation leads to symptoms associated with photoaging like thickening, wrinkling, and laxity, especially in areas chronically exposed to the sun like the face, neck, and backs of the hands (Gromkowska‐Kępka, 2021).
The mechanisms by which UVA radiation causes photoaging include: the generation of reactive oxygen species (ROS) that damage cell membranes, proteins, and DNA; degradation of collagen and elastin fibers in the dermis that provide structural support and elasticity; and the release of enzymes like matrix metalloproteinases that further break down collagen (Amaro-Ortiz, 2014). Chronic UVA exposure can also lead to pigmentary changes like uneven skin tone and age spots.
The effects of photoaging from UVA radiation accumulate over time and cannot be reversed. Protective measures like wearing sunscreen, hats, and protective clothing are important to minimize UVA exposure and prevent premature skin aging.
UVB Radiation
UVB radiation has wavelengths from 280-320nm and it primarily affects the outer layers of skin, called the epidermis 1. It is the main cause of sunburn and damages surface skin cells like keratinocytes 2. Prolonged exposure to UVB radiation leads to DNA damage and can cause skin conditions like sunburn, accelerated skin aging, and skin cancer. UVB rays are strongest during summer months and between 10am-4pm when the sun is at its peak 1. To protect against UVB radiation, it is recommended to use broad spectrum sunscreens, wear protective clothing, and limit sun exposure during peak hours.
UVC Radiation
UVC radiation has the shortest wavelength and highest energy in the ultraviolet spectrum. It is absorbed by the ozone layer and does not reach the Earth’s surface (“Ultraviolet (UV) Radiation.” U.S. Food and Drug Administration, 19 Aug. 2020). Because of this, UVC exposure from the sun is not a concern for humans. However, artificial UVC light is sometimes used for germicidal purposes, as it can damage DNA and kill microorganisms (McGreer et al., 2021). Direct exposure to skin and eyes should always be avoided.
The germicidal properties of UVC radiation make it effective at sterilization. UVC breaks molecular bonds within DNA and RNA, preventing replication and inactivating viruses, bacteria, and protozoa. For this reason, UVC lamps are sometimes used to disinfect surfaces and kill pathogens.
Infrared Radiation
Infrared radiation, also known as infrared light, is part of the electromagnetic spectrum and has a longer wavelength than visible light. It consists of light from 700 nanometers (nm) to 1 millimeter (mm) that humans cannot see but can detect as heat (1). When infrared radiation is absorbed by the skin, it causes molecules to vibrate and generate heat, leading to an increase in skin temperature (2).
Studies show that frequent exposure to intense infrared radiation can be damaging to the skin. Infrared rays have been shown to penetrate deep into the dermis layer of skin, causing the destruction of collagen and elastin fibers which provide structure and elasticity (3). This leads to accelerated skin aging and wrinkling over time. According to research, infrared radiation can also induce hyperpigmentation and proliferate pigment-producing cells known as melanocytes (1,2).
In addition, infrared radiation is capable of generating reactive oxygen species which cause inflammation and DNA damage (3). This oxidative stress contributes to photoaging and also increases the risk of photocarcinogenesis or skin cancer (2,3). Although infrared radiation has less energy than UV radiation, chronic exposure without protection still poses threats to skin health. Proper clothing, hats, and sunscreen can help prevent the harmful effects of infrared radiation on skin.
Visible Light
Visible light is the portion of the electromagnetic spectrum that is visible to the human eye. While visible light enables us to see, it can also cause damage to the eyes with prolonged exposure.[1]
The retina is especially vulnerable to damage from visible light exposure. Studies show that lifetime exposure to visible light contributes to eye diseases like age-related macular degeneration.[2] Blue light, in particular, has enough energy to cause photochemical damage to retinal cells over time.
One of the main ways visible light damages the eyes is through the formation of cataracts. A cataract is a clouding of the clear lens of the eye, causing blurred vision. Ultraviolet radiation is thought to be a major contributor to cataracts, but visible light also plays a role.[3] With excessive visible light exposure, oxidizing chemicals are created in the eye that can damage the lens proteins over time, leading to clouding.
Wearing sunglasses that block 99-100% of UVA and UVB light offers some protection against cataracts and other visible light damage. Reducing exposure to bright indoor lights, TV and device screens, and natural sunlight can also minimize the risks of eye diseases from visible light sources.
Immune System Effects
Exposure to UV radiation can suppress the immune system by inhibiting the proper functioning and response of the body’s defenses against viruses, bacteria, and foreign pathogens (Maglio, 2016). Studies show that UV rays, especially UVB, can diminish immune surveillance and allow for the reactivation of latent viral infections such as herpes simplex (Schwarz, 2005). The skin’s Langerhans cells, which are part of the immune system, are damaged by UV radiation. This makes it harder for the immune system to detect invading microbes and activate T-cells to fight infection.
Additionally, UV exposure triggers the release of immunosuppressive cytokines in the body that inhibit normal immune response. By suppressing cell-mediated immunity and antigen presentation, UV radiation prevents the immune system from properly recognizing and eliminating abnormal cancerous cells (EPA). There is evidence that overexposure to sunlight can reactivate certain viruses like herpes simplex, varicella-zoster, and Epstein-Barr.
DNA Damage
Exposure to UV radiation, especially UVB rays, can cause direct damage to DNA molecules in skin cells [1]. When DNA absorbs UVB energy, it can cause covalent bonds within the DNA molecule to break, creating defects called pyrimidine dimers. This damage can lead to errors during DNA replication and cause mutations in the DNA sequence [2]. These mutations accumulate over time and can lead to uncontrolled cell growth and eventually skin cancer.
One of the most common mutations caused by UV radiation is called a C>T or CC>TT transition mutation. This is when cytosine bases fuse together and pair incorrectly with thymine bases instead of guanine during replication. Studies of the genomes in skin cancers like melanoma have found high frequencies of these transition mutations, implicating UV radiation as the cause [3]. Preventing DNA damage from UV exposure is crucial to reducing risk of skin cancer.
In addition to directly damaging DNA, UV radiation also generates reactive oxygen species (ROS) that can indirectly damage DNA and proteins. ROS form when UV energy is absorbed by molecules in skin cells, creating free radicals that can further destabilize DNA. Minimizing UV exposure protects skin cells from accumulating DNA damage over time.
Prevention
The best way to prevent the harmful effects of solar radiation is to limit your exposure through protective measures such as sunscreen, clothing, and avoiding peak sunlight hours. According to the CDC, sunscreen is an essential protective measure against solar radiation (https://www.cdc.gov/cancer/skin/basic_info/sun-safety.htm). Apply broad spectrum sunscreen with an SPF of 15 or higher generously before going outside, even on cloudy days. Reapply every two hours and after swimming or sweating. In addition to sunscreen, cover up with clothing when possible. Wear long sleeves, pants, hats with wide brims, and sunglasses (https://www.cdc.gov/nceh/features/uv-radiation-safety/index.html). Tightly woven fabrics provide more protection from UV rays. It’s also important to avoid being outside during peak sunlight hours between 10am and 4pm, when solar radiation is strongest.
Summary
Solar radiation can have varied effects on the human body. The different types of solar radiation interact with the skin and eyes in unique ways.
UVA radiation ages skin cells and suppresses the immune system. UVB radiation causes sunburns and directly damages DNA which can lead to skin cancer. Though most UVC is absorbed in the ozone layer, any exposure can cause severe burns.
Infrared radiation warms the skin and, in high doses, can cause heat-related illnesses. Visible light enables vision but intense exposure can damage the eyes.
To limit the harmful effects of solar radiation, people can wear sunscreen, protective clothing, eyewear and limit time in midday sun. Through safe sun practices, you can enjoy the outdoors while reducing risk of cancer, aging and other damage from the sun’s rays.
