Sunscreens — Protecting the Skin from Sun Damage
July 1, 2012 5 minutes read
Special Feature
Sunscreens — Protecting the Skin from Sun Damage
By Terry Conroy, RPh
Terry Conroy is a practicing pharmacist and member of the medical team for AmeriCares, the humanitarian and disaster relief organization headquartered in Stamford, CT
Ms. Conroy reports no financial relationships to this field of study.
The skin's absorption of certain frequencies of ultraviolet radiation (UVR) induces biological effects that can result in acute and chronic photodamage of the skin. The acute effects are tanning, sunburn (erythema or redness of the skin), synthesis of vitamin D and the chronic effects involve mutation of DNA and immunosuppression that results in photoaging and photocarcinogenesis [the effect of ultraviolet irradiation in producing cancers].1 According to the American Cancer Society there are more than 2 million cases of basal and squamous-cell carcinoma diagnosed in this country each year.2 Just as alarming is the 2007 CDC report that 8,461 people died in the US from melanoma, a particularly aggressive form of skin cancer, while an additional 58,000 cases were diagnosed.3
The UVR effects on skin depend primarily on the wavelength of ultraviolet light, the length and intensity of exposure, repetition of exposure, age at time of exposure, site of exposure, and genetic factors present in the exposed individual.4 The wavelengths that are the major culprits are referred to UVA-I, UVA-II and UVB. UVB is responsible for causing sunburns, wrinkling, epidermal growth or hyperplasia, collagen damage and skin cancers.5 UVA wavelengths can penetrate deeper into the skin and damage DNA thus promoting the carcinogenic effects of UVB. UVA wavelengths differ from UVB wavelengths in that they are still biologically active having passed through clouds and glass and are responsible for triggering photo-drug reactions.6 The most intense exposure to UVR occurs during the summertime between 10 am-2 pm, at higher altitudes and when reflected off of water, sand, snow and ice which magnify the effect. UVR absorption is also increased on wet skin because moisture on the skin decreases reflection of UVR.
Blocking UVR absorption may be accomplished by avoiding the sun, wearing clothes that cover the head and body or by using topical sunscreens. The two major types of topical sunscreens are chemical and physical blockers. Chemical blockers provide protection by absorbing UV radiation, and physical blockers reflect or scatter UV radiation. The term broad-spectrum sunscreen indicates protection from both UVA and UVB wavelengths. There is no specific measurement for the effectiveness of UVA protection. In the case of protection from UVB wavelengths the sun protection factor (SPF) measures the effectiveness of a topical sunscreen. The SPF, determined in a laboratory, is the amount of UV radiation required to cause sunburn on skin with the sunscreen on, as a multiple of the amount required without the sunscreen. For example, a person who normally burns within 11 minutes of sun exposure could expect to extend that time period to 110 minutes with a SPF of 10 (11 minutes X SPF 10 = 110). The amount of UV radiation blocked by sunscreen is not directly proportional to the SPF. Therefore, SPF 30 doesn't block twice as much UV as SPF 15. It is known that SPF 15 blocks 93% UVB and SPF of 30 blocks 96.7% and to 40 blocks 97.5%.
The efficacy of sunscreens with a SPF > 15 for reducing the risks of skin cancers and photoaging is so well documented that the USFDA regulates the monographs and labeling of all topical sunscreens. The FDA has approved new labeling rules that will go into effect June 2012 pertaining to claims related to efficacy and water resistance.7 The new rules prevent the terms "sunblock", "sweatproof" and "waterproof" being used on labels. However, if applicable, the term "water resistant" may be used. The new rules alert consumers to whether a product is broad spectrum and provides protection from both UVA and UVB. It also distinguishes between SPF values greater than and less than 15 by highlighting the effectiveness of broad-spectrum sunscreens > 15 in reducing the risks of skin cancers and early aging and alerting consumers that SPF< 15 products may prevent sunburns, however, they do not prevent skin cancers or early skin aging.8
The prevention of "photo-toxicities" should begin in childhood and continue throughout a lifetime. Children have lower protective melanin levels and thinner skin than adults putting them at greater risk of sun damage.9 There is strong evidence suggesting that the risk of developing skin cancers in one's lifetime increases significantly with the number of sunburns that occurred during childhood. Limiting sun exposure between 10 am-2 pm and following the sunscreen tips below will provide the extra protection in reducing the damaging effects of the sun on the skin.
- Choose broad-spectrum sunscreen (UVB-UVA protection) with a SPF > 15.
- Liberally apply sunscreen to all exposed areas. Under-application and uneven application of sunscreens result in photodamage. Usually temple, ear, lips and posterior neck are undertreated and underprotected.
- Allow sunscreen to bind to the skin. Generously apply it at least 30 minutes before sun exposure. Products that contain PABA [para-aminobenzoic acid] or padimate O should be applied up to two hours in advance.
- Use water resistant sunscreens when swimming or if sweating.
- Reapply all sunscreens after swimming, heavy sweating, toweling off and every 2 hours even on cloudy or overcast days.
- Reapplying sunscreen will NOT extend the sun protection time period. For example a person using a SPF 20 can only stay in the sun 20 times longer than he/she could without sunscreen. The reapplication does not start the clock over and will not extend the burn-free time to 40 times longer.
- Limit sunscreen use in infants less than 6 months of age. Infants younger than age 6 months should be outfitted with hats and protective clothing and should be kept in the shade. Sunscreens in this age group should be limited to small areas of skin only, because an infant's skin is thin and chemically sensitive.
- Suncreens should be used as early as possible after six months of age. Physical blockers such as zinc oxide/titanium dioxide are preferred for children because they are difficult to wash/rub off and do not degrade in the sun.10 Therefore, they do not need to be reapplied with as great frequency as do chemical sunscreens. n
References
- Krakowski AC, et al. Chapter 14 Exposure to Radiation from the Sun. Auerbach: Wilderness Medicine 6th ed © 2012 Mosby an imprint of Elsevier Retrieved from 4-2-2012 MD Consult online database: http://www.mdconsult.com
- Learn About Skin Cancer American Cancer Society available at: http://bit.ly/bdDaVc [Accessed on April 3,2012.]
- Skin Cancer Center for Disease Control and Prevention available at: http://1.usa.gov/11FIFx [Accessed on April 5, 2012
- Krakowski AC, et al. Chapter 14 Exposure to Radiation from the Sun. Auerbach: Wilderness Medicine 6th ed C 2012 Mosby an imprint of Elsevier Retrieved from 4-2-2012 MD Consult online database: http://www.mdconsult.com
- Habif T. Clinical Dermatology, 5th ed. Chapter 19: Light-Related Diseases and Disorders of Pigmentation © 2012 Mosby 2012 Retrieved from 4-2-2012 MD Consult online database: http://www.mdconsult.com
- Clinical Dermatology Chapter 19: Light Pigmented Disorders © 2012 Mosby Retrieved from 4-2-2012 MD Consult online database: http://www.mdconsult.com
- U.S. Food and Drug Administration website: http://1.usa.gov/kSbTDY [Accessed April 4, 2012.]
- Questions and Answers: FDA announces new requirements for over-the-counter (OTC) sunscreen products marketed in the U.S. FDA website: http://1.usa.gov/mkyaQn [Accessed April 3, 2012.]
- Rudy, S, Skin Care for Infants and Young Children: Using new Evidence to Address Common Myths Medscape Pharmacist Education: http://bit.ly/jMDNBI [Accessed April 3, 2012.]
- Klein J, Chapter 99. Children in the Wilderness. In Auerbach: Wilderness Medicine, 6th ed. 2012 Mosby imprint Elsevier Retrieved from 4-3-2012 MD Consult online database: http://www.mdconsult.com
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