Protection against overexposure to sunlight is best achieved by a combination of physical and chemical means. These include sun avoidance, shade, clothing, hats and sunscreens.
Solar radiation at the Earth's surface encompasses ultraviolet radiation, which is harmful to skin; visible light, which allows us to see and plants to grow; and infrared radiation, which gives us a feeling of warmth. The daily ambient erythemal UV in northern Europe (50-60ºN) shows a clear sky summer to winter ratio of about 40:1, with day-to-day variations as a result of cloud cover.
The UV exposure of people depends not just on ambient values but as importantly on seasonal and social variations in behaviour. The result of this is that adult indoor workers in northern Europe receive half their annual sun exposure in about 30-40 days per year.
In people with white skins living in the tropics (30ºN to 30ºS), sun protection is necessary all year, whereas for those living in temperate latitudes (40ºN to 60ºN) sun awareness is generally limited to the six month period April to September.
Diffey BL. Sun Protection. Nederlands Tijdschrift voor Dermatologie & Venereologie, 9, 333-334.
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