Ultraviolet or UV is a form of electromagnetic radiation and an electromagnetic wave that sits after the visible light and before x-rays in the electromagnetic spectrum. It has a wavelength that ranges from 10nm to 400nm and frequencies ranging from 30 PHz to 750 THz. Note that the spectrum consists of other forms of electromagnetic radiation ranging from extreme low-frequency radio waves and extreme high-frequency microwaves to gamma radiation.
The Sun is the primary source of UV radiation on Earth. About 10 percent of the total electromagnetic radiation output of the Sun is ultraviolet. Artificial sources include incandescent lamps, gas-discharge lamps based on argon, mercury, and xenon, excimer laser, and ultraviolet light-emitting diodes, among others.
Prolonged and excessive exposure to this radiation is dangerous to organisms. Furthermore, prolonged sun exposure has been linked to numerous health-related effects in humans due to the harmful effects of UV radiation. These issues include skin damages such as sunburn and photoaging, skin cancers, damages to the eyes, and immune-related disorders.
Explainer: How UV Radiation Damages the Skin and Causes Cancer
To understand why UV radiation is dangerous to human health, it is important to take note of the following characteristics and facts about this form of electromagnetic radiation:
• Ultraviolet carries more radiant or photon energy than visible light. Photon energy is the energy carried by a single photon. In general, the amount of energy carried by a photon is directly proportional to its electromagnetic frequency and inversely proportional to its wavelength. Because UV rays have shorter wavelengths and higher frequencies than the visible light, infrared, microwaves, and radio waves, it carries more photon energy.
• There are different subtypes of ultraviolet radiation. Two subtypes are particularly critical when it comes to understanding the adverse effects of sunlight exposure. These are UVA and UVB rays. The Sun emits UVC rays, but the ozone layer and atmosphere absorb them. However, artificial sources such as arc welding torches, mercury lamps, and ultraviolet sanitizing lamps.
• Nevertheless, because UV has higher energy than visible light, it is more damaging. The damage transpires at the molecular level. To be particular, when a photon of UV is absorbed into the skin, it excites an electron that constitutes a skin cell. An electron at a high energy state disrupts internal cellular functions and processes to include cellular repair, replication, and metabolism, among others.
Disrupted cell functions cause different negative effects on the skin, as well as in overall skin and human health. Take note of the following:
1. Collagen Breakdown
Ultraviolet radiation breaks down collagen fibers to create visible signs of aging, such as wrinkling and sagging. The result is a condition called photoaging.
Specifically, when UVA penetrates the dermis, it induces damages that cause an abnormal buildup of elastin called elastosis. A high accumulation of elastin causes the production of enzymes called matrix metalloproteinases that break down collagen.
Elastosis fundamentally results in elastin replacing collagen. Note that collagen provides strength and rigidity, while elastin provides elasticity. Both are important in maintaining the firmness and tightness of the skin.
2. Retinol Depletion
Excessive exposure to both UVA and UVB also results in Vitamin A or retinol deficiency in the skin. Both UVA and UVB block the ability of the skin cells to recognize retinoic acid and synthesize retinol. Repeated exposure depletes epidermal retinol.
Depletion due to UVB exposure is based primarily on oxidative stress, while depletion due to UVA exposure comes from a photochemical reaction. The process is readily revisable if retinol depletion is due to the effects of UVB,
Retinol is essential in the formation of collagen fibers and blood vessels, as well as in maintaining an even skin tone by lessening dark spots and hyperpigmentation. Note that retinol also provides a protective action against UVB.
3. RNA Damage and Sunburn
UVA and UVB also have different effects on the skin and overall human health. UVB causes different types of damage to the ribonucleic acid or RNA. These include photochemical modification, crosslinking, and oxidative damage.
Furthermore, sunburns are due to UVB irradiation. A particular sunburn is simply an inflammatory response to RNA and DNA damages. For example, a photon of UVB can damage a single molecule in the RNA called U1 when absorbed by the skin.
A damaged U1 RNA creates an immune response characterized by the production and migration of signaling molecules called cytokines to the affected area that, in turn, signals the migration of more leukocyte-rich blood, thus causing redness, heat, and pain.
4. Free Radicals and Cancer
UV radiation indirectly and directly damages the deoxyribonucleic acid or DNA in skin cells that can result in basal-cell carcinoma, squamous-cell carcinoma, and malignant melanoma. Indirect damage transpires when UVA and UVB produce free radicals in cells. Note that free radicals are unstable hydroxyl and oxygen molecules with a missing electron.
Because electrons are found in pairs, these radicals scavenge for missing electrons from other molecules. Electron scavenging can damage cells at the molecular level, thus altering their genetic material. Altered DNA can lead to replication errors and cell mutations.
UVB radiation can also cause direct damage to the DNA by distorting its shape. Unfixed distortions can lead to a buildup of errors and cellular mutations. When these mutations transpire in a melanocyte, a melanin-producing skin cell, they can result in a dangerous type of skin cancer called malignant melanoma.
Protection: Using Sunscreens Against the Harmful Effects of UV Radiation
Humans evolved under constant exposure to sunlight. Hence, the body has a built-in mechanism for protecting against ultraviolet radiation and repairing the damages caused by prolonged and repeated exposure. Of course, the body can only do so much.
Serious diseases and cancers due to UV exposure are inevitable if the amount of ultraviolet radiation exceeds biological protective capacity, and if the damages outweigh the capacity to repair. For this reason, proactive actions are needed to complement the biological capabilities of the human body.
In considering how UV radiation damages the skin, causes skin cancer, and induces other adverse health effects, experts have recommended the use of sunscreens. These skincare products work by either physically blocking ultraviolet radiation, chemically absorbing them before they penetrate the skin, or both.
Physical sunscreens use mineral compounds such as titanium dioxide and zinc oxide as their main active ingredients. On the other hand, the formulation of chemical sunscreens is based on organic chemicals that primarily absorb and neutralize UV.
When choosing a sunscreen, it is important to pick one that provides broad-spectrum protection, considering that both UVA and UVB can damage the skin and affect overall human health. Furthermore, it is also vital to check the labels for the indicated protection ratings.
FURTHER READINGS AND REFERENCES
- Sorg, O., Tran, C., Carraux, P., Didierjean, L., Falson, F., and Saurat, J.-H. 2002. “Oxidative Stress-Independent Depletion of Epidermal Vitamin A by UVA.” Journal of Investigative Dermatology. 118(3): 513-518. DOI: 1046/j.0022-202x.2002.01674.x
- Törmä, H., Berne, B., and Vahlquist, A. “UV Irradiation and Topical Vitamin A Modulate Retinol Esterification in Hairless Mouse Epidermis.” Acta Dermato-Venereologica. 68(4): 291-299. PMID: 2459873
- Tyrrell, R. M. 1995. “Ultraviolet Radiation and Free Radical Damage to Skin.” Biochemical Society Symposia. 61: 47-53. DOI: 1042/bss0610047
- Wurtmann, E. J. and Wolin, S. L. 2009. “RNA Under Attack: Cellular Handling of RNA Damage.” Critical Reviews in Biochemistry and Molecular Biology. 44(1): 34-49. DOI: 1080/10409230802594043