Skin cancer and solar ultraviolet radiation

Managing exposures to ultraviolet (UV) radiation from the sun is one of the most effective ways of reducing the risk of skin cancer. Control of UV exposures includes both short-term benefits (i.e., prevention of sunburned skin) and long-term benefits (i.e., reduced skin cancer risk).

But while the motivation to avoid sunburns can be quite high, depending in part on your susceptibility to skin reddening, the motivation to prevent skin cancer years into the future may not be as strong because the benefits are uncertain. But the good news is that skin–cancer prevention can be incorporated into your daily skin–care practices so that you enjoy both the immediate benefits of healthy skin now as well as a reduced risk of skin cancer in the future.

Let’s briefly review some background information on the types of skin cancer and related UV exposures.

Types of Skin Cancers

• Basal cell carcinoma (BCC) originates in the basal cells of the epidermis, primarily in areas that are exposed to sun such as the head and neck. Although it is the most common type of skin cancer, it doesn’t usually metastasize or spread to other organs and is rarely fatal if properly treated.
• Squamous cell carcinoma (SCC) is a skin cancer that starts in squamous cells or the flattened cells present in the outer layer of skin. This cancer is less common than BCC, but it can be more invasive if untreated and in some cases can be fatal. Skin lesions from SCC are normally found on sun-exposed areas of the body. Basal and squamous cell carcinomas are often referred to as Nonmelanoma Skin Cancers (NMSC), and they typically occur in people older than 50 years. In 2006 there were over 2 million medical treatments for these NMSCs among the US Medicare population (Rogers et al. 2010).
• Cutaneous melanoma (CM) is the rarest of the three primary types of skin cancer, but it is the most dangerous if untreated. This cancer forms in melanocytes located in the basal layer of the epidermis.  Unlike BCC and SCC, which are concentrated on the head and neck, cutaneous melanoma is capable of developing anywhere on the body, such as on the trunk of the body and legs.

Skin cancer and ultraviolet radiation

Ultraviolet radiation (UVR) reaching the earth’s surface from the sun consists of UVA (wavelengths of 315 to 400 nm) and UVB (280-315 nm) electromagnetic radiations. Ultraviolet B radiation is more energetic that UVA, but UVA penetrates deeper into the skin. Both UVA and UVB radiation have been shown to damage dermal DNA (although by different mechanisms) and can also impact the skin’s immune system (Narayanan, Saladi, and Fox 2010).

Cumulative exposure to solar UVB radiation is the primary determinant of SCC, whereas BCC is a function of both cumulative and intermittent UVR exposures (e.g., sunburns)—particularly during childhood.  Cutaneous melanoma is related mainly to intermittent UVR exposures, but the relative roles of UVA and UVB are still debated (Moan et al. 2015).

Ultraviolet radiation (UVR) from the sun is grouped into two categories based on wavelength: UVA (315 to 400 nm) and UVB (280-315 nm). The biological effects of each UVR are not identical because the mechanisms of how they interact with skin tissue differ.

Susceptibility to Skin Cancer

Skin pigmentation is perhaps the most important physiological factor that controls skin cancer. The melanin pigment absorbs UV radiation irradiating skin and thus serves as a natural photoprotective agent (Brenner and Hearing 2008). Epidemiological studies have consistently shown that people with light skin have a greater risk of skin cancer than those with dark skin, which is consistent with the photoprotective properties of melanin.

Skin Cancer Prevention

Research conducted in Australia has demonstrated that regular sunscreen use reduces the risk of SCC and CM, but not BCC (Iannacone, Hughes, and Green 2014).  Failure to observe a protective effect for BCC may be due to the mechanism(s) by which basal cell carcinomas are induced. For example, if UV exposures during adolescence are an important determinant of BCC risk, then UV protection later in life may be less effective, even though BCC is related to cumulative UV exposures. Nevertheless, since BCC, SCC, and CM risks are moderated by UVR exposure, on-going UVR protection is important for the maintenance of healthy skin.

In addition to suncreen applications, there are a variety of other options that can be used to reduce UV exposures, including protective clothing, hats, and sunglasses. Moreover, limiting extended time in the sun to the early morning hours, for example, can drastically reduce UV skin irradiation–compared to the noontime hours!

The UV index, which is available in most weather apps, shows the magnitude or intensity of UV radiation, adjusted for the biological effectiveness of the different UV radiations. Use this index to manage your daily exposures to solar radiation.

Summary

• Exposure to ultraviolet radiation from the sun is a leading cause of skin cancers, including basal cell carcinoma, squamous cell carcinoma, and cutaneous melanoma—particularly in people with light colored skin.
• Routine monitoring of the Ultraviolet Index represents a core practice for maintaining healthy skin throughout the year!
• Protective measures to reduce UV exposures include the application of sunscreens as well as the use of hats, protective clothing, and sunglasses. Altering your daily schedule to avoid the highest UV levels during midday is also an option.

References

Brenner, Michaela, and Vincent J. Hearing. 2008. “The Protective Role of Melanin Against UV Damage in Human Skin.” Photochemistry and Photobiology 84: 539–49. doi:10.1111/j.1751-1097.2007.00226.x.

Iannacone, Michelle R., Maria Celia B. Hughes, and Adèle C. Green. 2014. “Effects of Sunscreen on Skin Cancer and Photoaging.” Photodermatology, Photoimmunology & Photomedicine 30: 55–61. doi:10.1111/phpp.12109.

Moan, Johan, Mantas Grigalavicius, Zivile Baturaite, Arne Dahlback, and Asta Juzeniene. 2015. “The Relationship between UV Exposure and Incidence of Skin Cancer.” Photodermatology, Photoimmunology & Photomedicine 31: 26–35. doi:10.1111/phpp.12139.

Narayanan, Deevya L., Rao N. Saladi, and Joshua L. Fox. 2010. “Review: Ultraviolet Radiation and Skin Cancer.” International Journal of Dermatology 49: 978–86. doi:10.1111/j.1365-4632.2010.04474.x.

Rogers HW, Weinstock MA, Harris AR, and et al. 2010. “Incidence Estimate of Nonmelanoma Skin Cancer in the United States, 2006.” Archives of Dermatology 146: 283–87. doi:10.1001/archdermatol.2010.19.