J.K. Rivers, MD, FRCPC
Dept. of Dermatology and Skin Science, University of British Columbia, and Pacific DermAesthetics, Vancouver, BC, Canada
Sun and UV Exposure
Ultraviolet (UV) light from the sun is the main environmental cause of photodamage and most skin cancers. Its damaging effects are cumulative, so daily protection throughout life is important.
- 70% of Americans are aware that daily sun exposure causes skin damage.[Fitzpatrick TB. Arch Derm 124:869-871 (1998).]
- Americans get <25% of their lifetime UV dose by 18 years of age. By the age of 60, they have absorbed 80% of their lifetime dose. [Godar DE, et al. Photochem Photobiol 77(4):453-7 (2003 Apr).]
- Use of sunscreens rose from 35% in 1986 to 53% in 1996.[Robinson JK, et al. J Am Acad Dermatol 37:179-86 (1997).]
- In a 2003 survey by the American Academy of Dermatology, only 47% of women and 33% of men reported using sunscreen regularly.[American Academy of Dermatology. 2005 Skin Cancer Survey Fact Sheet. URL: www.aad.org]
- More than half of teens are not too careful or not at all careful to protect their skin from sun exposure.[American Academy of Dermatology. 2005 Skin Cancer Survey Fact Sheet. URL: www.aad.org]
- Depending on locale and elevation, sunscreens should be considered for daily use throughout the year, not just in the hot summer months or during prolonged exposure.
- Many people are unaware that daily application is important to help prevent skin damage.
- Skipping sun protection on 1 day out of 4 can lower the skin’s defense mechanisms and increase photoaging effects.[Philips TJ, et al. J Am Acad Dermatol 43(4):610-18 (2000).]
- Two types of sunscreens:
- Organic or chemical, which protects against UV by absorbing the energy from UV rays.
- Inorganic or physical, such as metal oxides or particulate UV filters, which are insoluble particles that reflect UVA and UVB.
Sun Protection Factor (SPF)
- The SPF number indicates how much longer one can stay out in the sun before burning compared with having no protection.
- SPF relates to UVB protection only and does not indicate whether a product provides adequate protection from UVA rays. However, increasing SPF does generally correlate with increased UVA protection to some degree.
- There is general consensus among experts that daily, year-round, broad-spectrum photoprotection of at least SPF 15 is a key component of a sun-safe strategy to reduce cumulative lifetime exposure to solar UV.
- SPF is a lab assessment that does not generally reflect what’s used in the real world.
- SPF 15 is the minimum recommended level.
- It means that theoretically one can stay out without burning, 15 times longer than with no protection. However, this should not be used to encourage prolonged sun exposure.
- The level of UV filtration is not proportional to the SPF. The amount of UV transmission is 1/SPF so with an SPF of 2, 50% of UV light is transmitted. e.g., if you have an SPF of 30, you have blocked out 97% of UV light (1/30 transmitted).
- SPF products in lighter, esthetically pleasing formulations tend to be used more regularly and in sufficient quantity to deliver the intended UV protection.
- At present, there is no standardized test for UVA protection in North America.
- Different filters have different absorption profiles in the UVA range and they’re not all comparable. These filters must be carefully combined to provide photo-stable protection across the UVA spectrum.
- Some UV filters are degraded by sunlight and unless they’re chemically stabilized, they lose their effectiveness in a relatively short time.
- It is recommended to be applied 15-20 minutes before going outdoors and reapplied every 2 hours or after swimming/ heavy exertion.
- People typically use only half the amount they need for full protection.
- The recommended dose is 2mg/cm2 of skin, or 30ml (2 tablespoons) for the whole body, or 2.5ml (½ teaspoon) for 1 arm.
- Published studies indicate that the actual dose being used is much lower:
- 0.5mg/cm2[Bech-Thomsen N, et al. Photodermatol Photoimmunol Photomed 9(6):242-4 (1992-1993 Dec).]
- 1.0mg/cm2.[Stenberg C, et al. Arch Dermatol 121(11):1400-2 (1985 Nov).]
- In a week-long, double-blinded sunscreen usage test comparing consumer application habits when using SPF 30 vs. SFP 15:
- Heavy feeling products with a higher SPF were applied much more sparingly.
- Cosmetically formulated products with a lower SPF were used more consistently and in sufficient quantities to provide the intended protection. [Grosick TL, Tanner PR. Efficacy as used, not as tested, is true measure of sunscreen performance. Proceedings of the 62nd American Academy of Dermatology Annual Meeting; Feb. 6-11, 2004; Washington, DC, USA.]
- Most dermatologists recommend SPF 30. Those with higher SPF may have better UVA protection.
Sunscreens and Cancer
- Sunscreens are effective in protecting skin from actinic keratoses and squamous cell carcinomas.
- They have not been shown to reduce the incidence of a first basal cell carcinoma, but they may prolong the time to develop a second lesion.
- In a quantitative review of studies looking at sunscreen use and the risk for melanomas, Dennis et al. reported there was no association between these two factors.[Dennis LK, et al. Ann Intern Med 139(12):966-78 (2003 Dec).Ann Dec).]
The Vitamin D Controversy
The UV action spectra for DNA damage leading to skin cancer and for vitamin D photosynthesis are virtually identical. Consequently, the harmful and beneficial effects of UV irradiation are inseparable giving rise to the argument that sun avoidance (in order to prevent skin cancer) could compromise vitamin D sufficiency.[Wolpowitz D, et al. J Am Acad Dermatol 54(2):301-17 (2006 Feb).]
In order to analyze the risks/ benefits of sunscreens on vitamin D, Nash, et al. estimated the production of vitamin D based on measures of sunlight exposure and determined the impact of an SPF 15 sunscreen on vitamin D levels in humans. The study included 92 adult women located in 5 different geographic areas and found that the combination of diet and sunlight, even with daily use of an SPF 15 sunscreen provides adequate intake for vitamin D.[Nash JF, et al. J Am Acad Dermatol 52(3):161 (2005).]
- Avoid them.
- UV from the sun and from tanning beds can cause skin cancer and wrinkling.
- Consider using a self-tanning product instead.
- The main ingredient is dihydroxyacetone, hygroscopic white crystalline powder.
- Self tanning lotions and sprays offer a safe alternative to tanning.
- They develop color on the skin’s surface via a chemical reaction.
- They are not highly protective – most have an SPF of 3 to 4.[Draelos Z. Am J Clin Dermatol 3(5):317-8 (2002).]
- A sunscreen with an SPF of at least 15 (e.g., Olay® Complete, Anthelios® L or S, Neutrogena® Sensitive Skin Sunblock Lotion, Ombrelle®) should be used in association with self tanning agents.
Sunscreens serve an important role in overall sun protection. However, they should be used in conjunction with other sun protection measures such as clothing, hats and sunglasses.