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Health Effects of Exposure to Ultraviolet (UV) Radiation

 

 
  • Sunlight and its heat are essential to most of the familiar life forms. Exposure to UV radiation helps to create vitamin D in the body, which is essential in preventing disease. This radiation may also have a positive effect on skin diseases of various kinds, such as psoriasis and eczema
  
         
 
  • The harmful health effects of exposure to UV radiation include burns, accelerated aging of the skin, development of cataracts, damage to the conjunctiva, and various skin tumors (including malignant melanoma)
  
  • The highest personal exposure to UV radiation from an artificial source is sun beds. In 2009, the International Agency for Research on Cancer (IARC) classified UV-emitting tanning devices as 'carcinogenic to humans'
  

 

Ultraviolet Radiation – Introduction

Ultraviolet radiation is part of the electromagnetic spectrum in the wavelength range of 100-400 nm.

The UV range includes three main sub-ranges: UVA (wavelength of 315-400 nm), UVB (wavelength of 280-315 nm), and UVC (wavelength of 100-280 nm).

{The ISO-21348 international standard extends the ultraviolet radiation range to 10-400 nm and includes the shortest ultraviolet waves (121-10 nm).}

UVA and UVB radiation can be found within the wavelengths of non-ionizing radiation. The UVC radiation ionizes within part of this area (the shorter waves within it).

Most ultraviolet radiation is absorbed by the ozone layer. UVC radiation is absorbed entirely by the ozone layer and does not reach the earth's surface at all, while about 0.1% of the UVB radiation and 5% of the UVA radiation reach the surface of the earth.

The sun is the main source of human exposure to ultraviolet radiation. The degree of exposure depends on a variety of metrics such as geographical location, surface height, exposure time, season of the year, cloud coverage, and sun protection.

For example, during a sunny day on the Mediterranean coast, the ultraviolet radiation that reaches the earth's surface at midday is distributed to UVA of 95-96% and UVB of 4-5%.

In addition to the sun, there is also exposure to artificial sources that emit UV radiation, such as sun beds for cosmetic purposes, medical devices, fluorescent lights, electric mosquito killers, and industrial sources (e.g. lights for the entertainment industry).

Sunlight and its heat are essential for existence on Earth; however, exposure to ultraviolet radiation emitted from the sun or artificial sources emitting radiation can have harmful health effects.

 

 

Damage from Exposure to Sun and UV Radiation

Skin Structure and Function:

The skin is the largest organ in the body and protects the internal organs from injury, including UV radiation. The skin is composed of two main layers: the epidermis and the dermis.

The epidermis contains three types of cells: squamous cells (that produce keratin), basal cells and melanocytes (that produce melanin). Melanin can act as a physical barrier that dispenses the ultraviolet radiation as well as a filter that absorbs about 50-75% of the photons of the UV radiation. As a result of the melanin activity, penetration of the ultraviolet radiation decreases through the epidermis.

The dermis contains blood cells, lymph nodes, hair follicles, fatty glands, sweat glands, and connective tissue.     

Skin Damage

  • Burns — UV radiation can cause burns characterized by an immediate inflammatory response that includes, among other things, skin redness (erythema), edema, feeling of heat, itching, and pain in the affected skin area. The degree of skin redness after exposure to a particular dose of UV radiation depends on the sensitivity of the skin, the wavelength, the duration of exposure, and pigmentation of the skin (light skin burns more easily than dark skin). Erythema occurs about 3-5 hours after exposure to ultraviolet radiation, reaches its peak 8 to 24 hours after exposure and wanes in 3 days. In its severe form, erythema causes inflammation, blisters, and skin peeling.
  • Skin aging — chronic sun exposure accelerates the aging process. UVA radiation penetrates the deeper layers of the skin, damages the connective tissue, and is responsible for premature appearance of skin aging, including pigmentation, wrinkles, laxity and dryness. Skin aging is usually seen in the face, neck, and back of the hands, which are the areas exposed to the sun. One of the mechanisms proposed for skin aging as a result of exposure to UVA is the creation of free radicals.
  • An example illustrating the long-term damage of ultraviolet radiation can be found in the picture of a truck driver at the following link: http://www.nejm.org/doi/full/10.1056/NEJMicm1104059#t=article. The driver in the picture was exposed to the UV radiation with only one side of his face during his 28 years of work.  In the picture, we can see a comparison between the radiation-exposed side (without protective means) and the non-exposed side. The UVA radiation that passed through the glass window of the vehicle penetrated the epidermis and the upper layers of the dermis of the left side of his face, which was near the window, and as a result his facial skin thickened and wrinkled.  On the other hand, the right side of his face was not exposed to radiation and thus was not hurt.
  • Damage to genetic material — Exposure to UVA and UVB radiation can damage DNA. According to the International Agency for Research on Cancer (IARC), UVB radiation is absorbed into DNA and can directly damage it and initialize the cancerous process. Although UVA radiation is not absorbed by DNA, it can indirectly damage it by creating free radicals.
  • Pre-malignant skin damage — chronic exposure to the UV radiation has been associated with the development of actinic keratosis: lesions appearing in those areas of the body that have been permanently exposed to the sun. Some of these lesions may turn to squamous cell carcinoma (SCC), a type of skin cancer.
  • Malignant skin damage – Cancerous tumors — Exposure to sun as well as to artificial sources emitting UV radiation (such as sun beds) is the main risk factor for skin tumors. People with light skin, pale eyes, blond or red hair, and people who tend to "burn" easily are at increased risk of developing skin tumors following exposure. Dark skinned people are at a lower risk of developing skin tumors than those with light skin because they have more melanin pigment, which protects them from UV radiation.
  • Non-melanoma skin cancer — a term that includes basal cell carcinoma and squamous cell carcinoma, which develop from the epithelial cells in the skin. Other skin cancers are rare.
    Incidence in the World: Assessing the incidence of non-melanoma skin cancer is challenging. Unlike most cancers reported to national cancer registration centers, the diagnosis and treatment of most non-melanoma skin cancers is performed by community physicians, sometimes without a histological diagnosis or referral to a specialist, and therefore are not included in the cancer registration report. Despite the above, reports of the incidence in several countries can be found: in Finland, for example, the reported incidence of non-melanoma skin cancer per 100,000 people is 55.4 in women and 62.3 in men; in England — 51.2 in women and 73.5 in men; and in Uruguay — 26.3 in women and 40.9 in men. It is important to note that those data should be treated with caution because there is almost certainly an underestimation of the incidence rates in these countries.
    Incidence in Israel: In a study conducted by Maccabi Healthcare Services and published in 2015, information was collected on patients diagnosed with basal cell carcinoma or squamous cell carcinoma. The information was based on histological reports and included about 1.7 million Maccabi members in Israel in 2006-2011.  The results of this study showed that the age-standardized rate of basal cell carcinoma (ASR) was 188 per 100,000 person-years (PY), while the incidence of squamous cell carcinoma was 58 per 100,000 person-years. A sharp increase in incidence with age was demonstrated in both types of carcinomas. The increase in the incidence of basal cell carcinoma, both among women and men, began in their 20s and increased considerably in men aged 60 and over. However, squamous cell carcinoma rates were consistently higher in men, with a marked increase in incidence among men in their late 40s.
  • Melanoma — Melanoma is defined as a malignant tumor of melanocytes, cells that produce pigment in the skin, which is the main organ of the disease occurrence. Melanoma is responsible for most skin cancer deaths, although it accounts for less than 5% of all skin malignancies.
    Incidence in the World: Most epidemiological studies show an increase in the incidence of melanoma among light-skinned populations over the past decades. The World Health Organization report published in 2003 shows that about 133,000 new cases are diagnosed every year. Nearly 80% of the cases were found in North America, Europe, Australia and New Zealand. The report also shows that the incidence of the disease is similar between men and women. Another World Health Organization report published in 2017 found that as of 2012, 230,000 new cases of melanoma were diagnosed worldwide. According to the organization, about a quarter of the new cases will result in death.
    Incidence in Israel: According to data published by the National Cancer Registry in Israel in 2012, the age-standardized incidence rate of skin melanoma (ASR) — invasive tumors — in the Jewish population was 12.08 and 9.62 per 100,000 per year for men and women, respectively. For in-situ tumors, the age- standardized incidence rate in the Jewish population was 4.99 and 3.44 per 100,000 per year for men and women, respectively. 

 

Vision Impairment

The human eye is partially protected from exposure to UV radiation due to its location and the activity of eyelids. This exposure depends on the time of day, season, weather, distance from the equator, and reflective surfaces in visual range.

The short waves (UVB) are mainly absorbed by the cornea. The longer waves (UVA) pass through the cornea, reaching the eye lens and retina. In fact, among adults only 1% or less of UV radiation reaches the retina.

There is strong evidence that exposure to UV radiation is associated with eyelid tumors; basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), as well as with other eye diseases, such as cortical cataract (a type of cataract characterized by the occurrence of peripheral lesions in the eye lens).

For information on sun exposure reducing measures

 

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Damages from Exposure to UV Radiation from Artificial Sources

Sun Beds

מיטת שיזוף

The highest personal exposure to UV radiation from an artificial source is sun beds. In a 2014 literature review and meta-analysis, the prevalence of sun beds was examined. The survey covered 88 articles from the United States, Central and Northern Europe and Australia, and included a population of approximately 400,000 participants. It was found that the prevalence of sun beds use was approximately 35% in adults, 55% among university students and about 19% among youth.

The intensity of the ultraviolet radiation emitted from tanning devices can be 10 to 15 times as strong as that from sun rays at noon. The bulbs in sun beds usually belong to two main categories: UVA-emitting bulbs and UVB-emitting bulbs.

In 2009, the International Agency for Research on Cancer (IARC) classified UV-emitting tanning devices as “carcinogenic to humans (Group 1). Today more than 40 national/regional authorities around the world prohibit and restrict the use of sun beds.

According to the literature review mentioned above, it is estimated that sun beds are responsible for approximately 450,000 non-melanoma cancers per year and more than 10,000 cases of melanoma in Australia and Europe.

In a literature review and meta-analysis of 31 articles published between 1990 and 2010, sun beds were found to be associated with a 16% increased risk of developing melanoma (95% CI 1.05-1.28). For the use of sun beds over 10 times throughout life, the relative risk was estimated at 34% (95% CI 1.05-1.71), while the use of sun beds for one year or less increased the risk of developing melanoma by approximately 37% (95% CI 1.06-1.77) . The relative risk of those who used sun beds for more than one year was estimated at 61%, although the excessive risk in this group was not significant (95% CI 0.98-2.67).

For information on the guidelines of the international health organizations regarding the use of sun beds and legislation in Israel

 

UV-based Nail Dryers

Nail drying lamps are used at home and in nail salons. These days, there are hundreds of UV-based nail dryers, most of which have UVA-emitting light bulbs (they may also emit UV-B and UV-C radiation in minimal amounts that could not be measured). The degree of exposure to UV radiation from a nail dryer depends on the type of device, the type of light source, the bulb intensity, and the number of bulbs in the device. It was found that the higher the bulb intensity, the higher the level of radiation emitted from the device.

The assessment of UV exposure levels using nail dryers has been performed only in a few studies. An article published in 2013 examined various nail dryers and found that upon exposure for less than 10 minutes, the hands absorb the amount of radiation equivalent to the upper limit of the exposure threshold recommended for a full day (8 hours) outdoor worker. In addition, the UV radiation dose of UV lamps corresponds to UV Index 6, which represents a high risk of injury due to unprotected sun exposure. However, it should be noted that the study evaluated only two types of UV lamps, and did not include statistical analysis. Another study, published in 2014, examined 17 nail dryers differentiated by brand, by the number of bulbs in the instrument, and by their wattage power. It was found that the higher the bulb intensity, the more UV radiation was emitted. Longer exposure times increased the potential for skin damage. However, the researchers believe that the risk of developing a cancerous process remains low even when there are multiple exposures to these devices.

Repeated exposure to UV radiation from nail dryers raises concerns about possible skin cancer risk. To the best of our knowledge, there have been no direct studies evaluating this risk. Due to the limited number of studies and their limitations, the recommendation is to reduce exposure as much as possible (by wearing fingerless gloves or by applying sunscreen to the hands during exposure).

 

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Beneficial Effects of Exposure to UV Radiation

Vitamin D is produced in the human body during exposure to sunlight, and is also found in foods such as fish and eggs. Vitamin D participates in many body processes associated with skeleton construction. In addition, studies show that vitamin D plays a role in protecting against various cancers (prostate cancer, breast cancer, colorectal (bowel) cancer) and autoimmune diseases such as type 1 diabetes, multiple sclerosis, and rheumatoid arthritis. The amount of sunlight required to obtain a sufficient level of vitamin D is estimated according to various models. These models calculate duration of desired stay outside based on geographical location, height, time of day, season of year, amount of melanin in the skin, cloud coverage, shade, and amount of light reflected from the ground.

UV radiation may play a role in immune system activity. According to the proposed mechanism, UV radiation protects against the development of autoimmune diseases by suppressing hyperactivity of the immune system (in autoimmune diseases, the body's immune system attacks other cells and is in a state of hyperactivity). There is evidence suggesting that UVB radiation increases the production of white blood cells of regulatory T-cell type in the immune system. Those cells have special importance in limiting the activity of other T cells, which attack cells and tissues of the body itself.

 

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29.7.2019