Sunscreens
The biological efficacy (erythema action) of the radiation is dependent on wavelength. The unit SED (standard erythema dose) is a direct measure of the erythema action of radiation. The skin by itself absorbs UV radiation depending on the thickness of str
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Sunscreens Hans Christian Wulf
Key Points
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The biological efficacy (erythema action) of the radiation is dependent on wavelength. The unit SED (standard erythema dose) is a direct measure of the erythema action of radiation. The skin by itself absorbs UV radiation depending on the thickness of stratum corneum and the degree of pigmentation. When testing SPF of a sunscreen in humans 2 mg/cm2 is applied, in real life much less sunscreen is used 0.5 mg/cm2. It has been suggested that the protection is reduced exponentially when a thinner layer is used. The number of sunburn cells, cutaneous DNA damage, conversion of urocanic acid, and immunosuppression are diminished by sunscreen use. Human studies have indicated that the number of actinic keratoses as well as squamous cell carcinomas can be reduced if sunscreens are used regularly.
21.1 Introduction The need for sun protection has increased considerably along with longer vacations, shorter working hours, and wealth in the society. This has resulted in travels to sunny destinations, sometimes several times a year, also in winter when the natural sun protection of the skin is low. The interest in sun protection seems to have been already prevalent during World War I and especially World War II when red veterinary petrolatum (red vet pet) and salicylates were used [40]. The first commercial available sunscreen was developed in 1928 and was used by the military during World War II [34, 40]. In 1935, Eugene Scheuller produced benzyl salicylate (Ambre Solaire) that gave good protection against erythema [40]. We had to reach the 1970th before the use of sunscreens became popular on holidays and on the beach, to avoid burning and scaling. Since then, sunscreens have developed further, not only to avoid sunburn by absorbing UVB, but also to protect against UVA, primarily to minimize wrinkle formation. Protection against skin cancer was assumed because of UVB absorption. At the same time, focus has also been on long-term safety with emphasis on stability, carcinogenesis, and hormone-disturbing properties.
21.2 Sunlight
H. C. Wulf Bispebjerg Hospital, University of Copenhagen, Department of Dermatol, D42, Bispebjerg Bakke 23 DK-2400 Copenhagen NV, Denmark e-mail: [email protected]
The spectral distribution of sunlight is dependent on the time of day, time of year, and the geographical location. In all places, the shortest wavelengths are found when the sun is in its highest position in the sky. However, even at the equator, the wavelengths at ground levels are longer than 295 nm. The biological
G. B. E. Jemec et al. (eds.), Non-Surgical Treatment of Keratinocyte Skin Cancer, DOI: 10.1007/978-3-540-79341-0_21, © Springer-Verlag Berlin Heidelberg 2010
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a
H. C. Wulf Erythema potential
Sun intensity (log)
10 1
-5 Summer
CIE
-6
Winter
0.1
-7
0.01
-8
0.001
-9
0.0001
b
100
280
300
CIE x SUN
320
340
360
380
-10 400
360
380
400
22. July
80 14. April
60 40 20
15. Dec.
effect of sunlight increases with higher sun altitude a
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