Faculty Peer Reviewed
At this point it seems that the general public is aware of the relationship between exposure to the sun and skin cancer. It is troubling, however, that our culture still considers a dark tan to be “healthy” despite the World Health Organization’s classification of ultraviolet light emitted from tanning devices as a human carcinogen, based on observational studies that show a 75% increase in cutaneous melanoma in people using tanning devices before age 35. Protection from the harmful ultraviolet (UV) radiation of the sun is something that deserves to be part of general preventive medicine, as approximately 39% of the United States population experiences at least 1 sunburn per year, and sunburn is a preventable major risk factor for skin cancer. A community-wide study in Nambour, Australia, found that “it is possible to implement the daily application of sunscreen in sun-exposed populations,” which indicates that educating patients regarding healthy sun practices is a primary prevention strategy that is both possible and beneficial.
What is UV light?
Ultraviolet light is electromagnetic radiation with higher frequency and shorter wavelength than visible light. The sun and tanning devices both emit UV light. It can be divided into UVA, which is further subdivided into UVA I and UVA II, and UVB. UVA I has the longest wavelengths (340-400 nm), UVA II has intermediate (320-340 nm), and UVB has the shortest wavelengths (290-320 nm). UVB radiation causes more damage to skin, but 10-100 times as much UVA radiation reaches the earth’s surface. UVB and UVA both contribute to photoaging of the skin, but UVB and UVAII are the major contributors to sunburn.
What can provide protection against UV light?
The best way to avoid UV light is to avoid direct sunlight, especially between the peak sun hours of 10 AM to 4 PM. UVB radiation is able to cause sunburn even on a cloudy day. Understandably, sun avoidance is neither feasible nor desirable for most people. The use of hats, sunglasses, and more covering clothing also provides protection against UV light, but again, for many this is a hard sell.
The use of sunscreen is the most feasible and generally accepted recommendation for protection against UV light. Sunscreens are available in two main types. “Sunblocks” are creams made of inorganic ingredients such as titanium dioxide or zinc oxide that sit on the surface of the skin and form a physical block preventing UV radiation from entering the skin. The other, more frequently used type of sunscreen are the chemical agents made of various organic compounds that absorb various wavelengths of UV light. A comparison study of ingredients in sunscreens has shown that agents containing a mixture of titanium dioxide, ecamsule, avobenzone, and 4-methylbenzylidene camphor provide the best overall protection.
To achieve FDA approval, sunscreens must block UVB and at least part of the UVA II spectrum. It is important to read the label of sunscreen carefully to determine what types of UV radiation it blocks, as the SPF may only refer to the UVB protection the product provides. It is also important to realize that sunscreen is most effective when used on a day-to-day basis, as “sunscreens probably prevent squamous cell carcinoma of the skin when used mainly during unintentional sun exposure,” as opposed to use only during sunbathing and long-duration outdoor activities. For those who are concerned about decreasing vitamin D levels by limiting UV light, sunscreen use and vitamin D deficiency have never been found to be associated.
What is SPF?
The sun protection factor of a sunscreen is the ratio of time required to produce minimal erythema (or reddening) of skin covered by a sunscreen product to the time required to produce the same degree of erythema without the sunscreen. It is important to remember that the SPF is determined experimentally in an ideal environment. SPF testing is done indoors using artificial light sources, which excludes many of the real-world conditions that lower SPF (wind, heat, humidity, altitude, water, and sweat). The SPF is determined using 2 mg of sunscreen per cm2. The problem is that most people apply sunscreen less liberally: at about 0.5-1 mg/cm2, with one study finding a median application amount of 0.79 mg/cm2.[3,4] This under-application of sunscreen drastically lowers the actual SPF; a sunscreen labeled as SPF 15 when applied at only 0.5-1 mg/cm2 has a true SPF effectiveness of only 3-7.
An SPF of 30 or higher is recommended by the American Academy of Dermatology. Regardless of the level of SPF used, frequent reapplication is the most important factor in preventing UV radiation damage from occurring. Paradoxically, 2 studies have shown that the use of higher SPF sunscreens leads to a greater amount of sun exposure, although a third study found no such correlation.[7,8,9] In general, sunscreen should be reapplied at least every 2-3 hours, regardless of SPF level.
Patient education regarding UV light exposure, including avoidance of tanning devices and proper protection against sunlight on a day-to-day basis, is both necessary and feasible. It should be stressed that tanning devices should never be used, sunscreen products of at least SPF 30 should be applied on a daily basis, and sunscreen should be reapplied frequently during sustained outdoor activities.
Courtney Maxey is a 3rd year medical student at NYU School of Medicine
Peer reviewed by Vicki Levine, MD, Chief Dermatology, Department Veterans Affairs New York Harbor Health Care System
Image courtesy of Wikimedia Commons
1. International Agency for Research on Cancer Working Group on artificial ultraviolet (UV) light and skin cancer. The association of use of sunbeds with cutaneous malignant melanoma and other skin cancers: a systematic review. Int J Cancer. 2007;120(5):1116-1122.
2. Brown TT, Quain RD, Troxel AB, Gelfand JM. The epidemiology of sunburn in the US population in 2003. J Am Acad Dermatol. 2006;55(4):577-583.
3. Neale R, Williams G, Green A. Application patterns among participants randomized to daily sunscreen use in a skin cancer prevention trial. Arch Dermatol. 2002;138(10):1319-1325. http://archderm.ama-assn.org/cgi/content/full/138/10/1319
4. Sunscreens: are they safe and effective? Med Lett Drugs Ther. 1999;41(1052):43-44. http://www.ncbi.nlm.nih.gov/pubmed/10368702
5. Bissonnette R, Allas S, Moyal D, Provost N. Comparison of UVA protection afforded by high sun protection factor sunscreens. J Am Acad Dermatol. 2000;43(6):1036-1038. http://journals1.scholarsportal.info/details.xqy?uri=/01909622/v43i0006/1036_coupabhspfs.xml
6. Vainio H, Miller AB, Bianchini F. An international evaluation of the cancer-preventive potential of sunscreens. Int J Cancer. 2000;88(5):838-842.
7. Autier P, Dore JF, Négrier S, et al. Sunscreen use and duration of sun exposure: a double-blind, randomized trial. J Natl Cancer Inst. 1999;91(15):1304-1309. http://jnci.oxfordjournals.org/content/91/15/1304.full
8. Autier P, Dore JF, Reis AC, et al. Sunscreen use and intentional exposure to ultraviolet A and B radiation: a double blind randomized trial using personal dosimeters. Br J Cancer. 2000;83(9):1243-1248.
9. Dupuy A, Dunant A, Grob JJ; Réseau d’Epidémiologie en Dermatologie. Randomized controlled trial testing the impact of high-protection sunscreens on sun-exposure behavior. Arch Dermatol. 2005;141(8):950-956. http://www.ncbi.nlm.nih.gov/pubmed?term=%2522R%25C3%25A9seau%20d’Epid%25C3%25A9miologie%20en%20Dermatologie%2522%255BCorporate%20Author%255D