What is UV radiation?  

The sun's ultraviolet (UV) radiation  is the most important source of UV radiation in the living environment. Exposure of the skin to large amounts of UV radiation and skin burn increase the risk of skin cancer. UV radiation can also damage the eyes. 

UV radiation is an electromagnetic wave. UV radiation has a wavelength of 100 to 400 nm (nm = nanometre). UV radiation is further subdivided into UVA, UVB and UVC according to wavelength. Of the solar UV radiation reaching the earth, 95% is UVA and about 5% is UVB. UVC is completely filtered out by the atmosphere.  

UVA penetrates the deepest layers of the skin, tanning the pigment in the skin and causing premature ageing.UVA radiation also promotes skin cancer.  

UVB radiation burns the skin. It penetrates the surface of the skin and causes it to thicken and tan.  The thickened layer of skin protects the tissues from the harmful effects of UV radiation, together with tanning, i.e. increased pigmentation. However, exposure of the skin to large amounts of UV radiation and skin burn increases the risk of developing skin cancer.  

UVC radiation is completely filtered out in the upper layers of the atmosphere. UVC radiation is very burning and is used, for example, in special lamps designed to kill bacteria. Read more about UV disinfection.  

The UV index describes the intensity of UV radiation 

UV radiation is more intense the higher the sun is shining. The UV index describes the intensity of UV radiation. The higher the UV index, the shorter the time your skin can withstand the sun without burning. The need for protection starts when the UV index is at least 3. A UV index of 3 can be reached at midday on the south coast from April to September. In mid-summer, the UV index can reach 3 or more between 10 a.m. and 5 p.m. The maximum UV index in Finland is 6 to 7 and can be reached on the southern coast in mid-summer at noon. In Mediterranean countries, the UV index is 8 to 10 in summer. At equatorial latitudes or in the mountains, the UV index can rise above 12.  

UV radiation is weak when the UV index is 0-2. Sun protection is not usually needed, but if you stay outdoors for very long periods of time, protection may be necessary.  

UV radiation is moderate with a UV index of 3-5 and strong with a UV index of 6-8. Protection is necessary. Get into the shade at midday, wear a shirt, use a sunscreen with a high sun protection factor (SPF) and wear a hat and sunglasses.  

UV radiation is very strong when the UV index is between 8 and 10 and extremely strong when the UV index is above 11. Avoid being outside at midday and seek shade when outside.  A shirt, sunscreen with a high sun protection factor (SPF), sunglasses and a hat are essential.  

Note: The recommendations apply for the daily maximum level of the UV Index when skies are cloudless.  

Caution: UV exposure on snow, water and at the beach (lucid sand areas) may be higher than the predicted maximum UV Index for that day. That’s because UV radiation is reflected from bright or reflective surfaces. Special attention should therefore be paid to sufficient sun protection in such situations.  

The Finnish Meteorological Institute's website provides a forecast of the UV index across the globe for the current day and the next two days. In addition to the forecasts, the service also provides the UV index values measured for the current day at Finnish observatories: Helsinki, Utö, Jokioinen, Jyväskylä, Kuopio, Sotkamo and Sodankylä.  

You can also check the forecast of the UV index in different parts of the world in the Finnish Meteorological Institute's Weather app. Read more about the UV index and check the UV index forecast.   

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