Dangers of the Sun Introduction Skin cancer is the most rapidly increasing form of cancer in the United States.1  National Cancer Institute estimates more than 1,000,000 new cases of skin cancer in the United States in 2009.2  About 65-90% of melanoma, the third most common type of skin cancer, is caused by ultraviolet (UV) light or sunlight exposure and researches show that most skin cancers can be prevented if people are protected by UV light.3 Ultraviolet Radiation The UV radiation spectrum can be divided into three bands: UVA, UVB, and UVC.4 Sunlight is m ostly composed of UVA, which is believed to damage the connective tissue and has been found to increase the risk of skin cancer.  UVB is mostly absorbed by the ozone layer, but still small portion of it reaches the earth's surface.4 UVB penetrates superficially into the epidermis and is the principal cause of sunburn reactions.5, 6  Although considered the most toxic, UVC is mostly absorbed by the ozone layer and hardly reaches the ground.4 Sunscreens Sunscreens contain active chemical ingredients that provide protection from the sun through absorption, reflection, and scattering of UV radiation.5 They are usually divided into two categories: physical (inorganic) and chemical (organic).4  Physical sunscreens are thick, opaque substances that prevent UV radiation from reaching the skin by scattering the sunlight.5 They contain titanium dioxide, zinc oxide, or talc as their active ingredients.5,7  These sunscreens are very effective in blocking both UVA and UVB radiation; however, they are messy and usually cosmetically unappealing.5, 7 Chemical sunscreens are the most commonly used and are available in a variety of formulations.5  They contain one or more of the UV absorbing chemicals.5  Some of the most widely used chemical groups that block UVB radiation are PABA (p-aminobenzoic acid), PABA esters (padimate O), cinnamates (cinoxate, ethylhexyl-p-methoxycinnamate), salicylates (octylsalicylate, homosalate), and anthranilates (methyl anthranilate).5, 7  While these all block UVB radiation, the chemical group known as benzophenone (oxybenzone and dioxybenzone) provides protection against both UVA and UVB.5 Sun Protection Factor (SPF) Sunscreens have been assigned Sun Protection Factor (SPF) values which is a number that refers to the sunscreen product’s ability to block UVB radiation.8  A sunscreen product with a SPF of 15 will protect your skin 15 times longer from UVB than if you did not have sunscreen applied.  The exact amount of time will vary from person to person, the altitude, and proximity to the equator. The efficacy of a product is related not only to its SPF but also to its resistance to water immersion and sweating.8  The following three labeling recommendations have been suggested to help clarify water/sweat protection7: Sweat-resistant: maintains SPF for at least 30 minutes of continuous heavy perspiration; Water-resistant: maintains SPF for at least 40 minutes of continuous water exposure; and Waterproof: maintains SPF for at least 80 minutes of continuous water exposure. It is recommended that sunscreens be reapplied after swimming or perspiring.9  Recommendations Centers for Disease Control and Prevention (CDC) provides following recommendations for sunscreen use9,10:  Avoid direct exposure beween the hours of 10am and 4pm.  If you have to be outdoor, remain under the shade and cover skin with protective clothing, such as broad-brimmed hats, long-sleeved shirts, long pants and sunglasses. Use a sunscreen product with a SPF of at least 15. Sunscreen products should be applied 20 to 30 minutes before going outside. Topical Toxicology The FDA recommends that sunscreens containing PABA should be avoided in children younger than six months of age, although a review of the oral use of aminobenzoic acid in large doses has shown it to be quite safe, even in young children.11 Sunscreens that contain PAPA and its esters can cause contact dermatitis or photosensitivity reactions.5  PAPA should be avoided in patients who are allergic to benzocaine, sulfonamides or thiazides. 12 Oral Toxicology Zinc oxide, an ingredient often found in physical sunscreens, can cause gastrointestinal irritation (nausea, vomiting or diarrhea) if swallowed.  Human overdose data on PABA or its esters are rare.  Nausea, vomiting, and abdominal cramps as well as metallic taste are often seen when ingested.  Ingestions of more than 10 grams per day for days have been necessary to induce symptoms other than local gastrointestinal irritation.13 Many sunscreen products contain a form of salicylate as their active ingredient, such as homomenthyl salicylate (homosalate).  Homosalate hydrolyzes in vivo to free salicylic acid and homomenthol.  Thus, homosalate-containing sunscreens can theoretically cause salicylate poisoning.  However, there are no such reported cases of salicylate intoxication resulting from ingestion or dermal application of sunscreens containing homomenthyl salicylate.14  Conclusion The risks of sun exposure and its relationship to skin cancer have been well documented.  Regular sunscreen use seems to help limit these harmful effects.  The risks of using sunscreen products appear to be minimal.  Therefore routine sunscreen use should be recommended in all individuals, especially children, exposed to the sun. Revised 11/2009 References 1. "Skin Cancer Statistics". Centers for Disease Control and Prevention [available at:www.cdc.gov/cancer/skin/statistics/index.htm  accessed on 11/2/09].   2. "Skin Cancer" National Cancer Institute, U.S. National Institutes of Health [available at: www.cancer.gov/cancertopics/types/skin          3. Centers for Disease Control and Prevention.  Guidelines for shcool programs to prevent skin cancer. MMWR 2002;51(No.RR-4):1-16. 4. "Basic Information About Skin Cancer". Centers for Disease Control and Prevention [available at www.cdc.gov/cancer/skin/basic_info/index.htm, accessed on 11/2/09].  5. Nicol NH. “What’s New With Sunscreens? Choices-Choices-Choices.” Pediatr Nurs. 1989;5(4):417-418. 6. Wiss K. “Lasers, Tissue Expansion, and Sun Protection in Pediatric Dermatology.” Cutis 1990;45:331-333. 7. Baron ED, Kirkland EB, Domingo DS. "Advances in Photoprotection." Dermatology Nursing. 2008;20(4):265-272. 8. Antoniou C. Kosmadaki MG, Stratigos AJ,  Katsambas AD. "Sunscreens - what's important to know." JEADV. 2008;22:1110-1119. 9. "Protecting Children from the Sun." Centers for Disease Control and Prevention [available at: www.cdc.gov/cancer/skin/basic_info/children.htm, accessed on 11/2/09]. 10. Centers for Disease Control and Prevention. Counseling to prevent skin cancer. MMWR 2003;52(No.RR-15):    13-17. 11. Hurwitz S. "The Sun and Sunscreen Protection: Recommendations for Children."  J Dermatol Surg Oncol. 1988;14(6):657-660. 12. Norins AL. “Sunscreens for Children.” JAMA. 255(20):2809, 1986. 13. Editorial Staff: Para aminobenzoic acid. In: Klasco RK (Ed): POISINDEX® System. Thompson Reuters, Greenwood Village, Colorado (Edition expires 12/2009). 14. Editorial Staff: Salicylates. In: Klasco RK (Ed): POISINDEX