Clothes – a cap or other hat with brim and a shirt – offer a good protection against UV rays. Also by staying in the shade from the direct light when the sun is high, you can easily halve your UV exposure. Even in the shade, it is good to take into account the reflection of UV rays from snow, water or sand, as well as the so-called diffuse radiation coming from the sky.

UV radiation penetrates clouds more easily than visible sunlight. Only low, thick clouds attenuate UV radiation effectively.

Thin clouds and a white snow field together create difficult conditions: in addition to direct radiation from the sun, there is a lot of diffuse radiation through the clouds, and both of these are also reflected from the snow.

Unfortunately no, because you only feel the heat radiation of the sun on your skin. Wind or chilly weather can evaporate the heat from your skin, but the UV index can be as high as on a hot day.

The skin does not forget the UV radiation it has received. The effects of the radiation accumulate in the skin’s memory throughout life.

Children’s skin is more sensitive to the harmful effects of UV radiation. Repeated sunburn or high lifelong UV exposure increases the risk of skin cancer in the future.

In southern Finland, the value of the UV index rises above the need for protection in midsummer between 10 a.m. and 5 p.m. In northern Finland, the time is one hour shorter at both ends. Although the radiation in the Mediterranean countries is stronger at noon than in southern Finland, the protection time is almost the same.

The shorter the shadow in the sunlight, the stronger the radiation. It is wise to seek shade at the latest when the shadow is shorter than your body when standing.

The skin can get burnt or tan in the spring sun in Finland as well. There is a risk of sunburn whenever the UV index reaches or exceeds the protection limit 3. In southern Finland this reading has been measured in some years as early as the end of March around noon. At the latest, readings of 3 can be measured in mid-September.

Sunscreen products can prevent sunburn, as they absorb the skin-burning UV radiation. However, you cannot prolong your stay in the sun by using sunscreen. Sunscreen should be used in sufficient quantity, but even then primarily for supplementing other protection.

The sunscreen must have at least a protection factor of 30. The protection must cover both UVB and UVA radiation. Sunscreen must be used in abundance and reapplied often enough.

There are considerable differences in tolerance to UV radiation between different groups of people. Light-skinned and red-haired people are particularly sensitive to radiation, as are children.

A tan does not protect the skin from burning. A tan only corresponds to a sunscreen protection factor of 4 at most. UV rays can penetrate even tanned skin and damage tissue. The skin does not toughen from sunburns, in fact the opposite happens. Especially protecting a child’s skin from repeated sunburn significantly lowers the risk of skin cancer in adulthood.

The UV index, or UVI, indicates the amount of harmful UV radiation from the sun. The variation of the UV index is primarily influenced by the location on the globe and the time of year and day. The biggest factor affecting the solar UV radiation reaching the Earth’s surface is the sun’s elevation angle, which determines how long the sunlight travels through the atmosphere. The journey is shorter the more perpendicularly from top to bottom the sun shines. The elevation angle varies on Earth by latitude and by year and time of day. At noon, the sun is at its highest, and then there is more UV radiation.

The UV index on Earth varies between 0−20. In the tropics, the UV index does not vary much, remaining above ten throughout the year. At Mediterranean latitudes, the highest UV index values are the same as in the tropics, and in winter the lowest values are less than four. At Finland’s latitude, the UV index rises to around six in the summer, but there is almost no UV radiation in the winter.

In addition to the elevation angle of the sun, the UV index is affected by cloudiness, height above sea level, the reflectivity of the land or sea surface and the amount of ozone in the atmosphere.

The Finnish Meteorological Institute measures UV radiation in 7 locations in Finland. The observation sites have been selected so that they cover the whole Finland as well as possible. The southernmost measuring station is in Utö and the northernmost in Sodankylä. It has been decided to prepare the forecasts for the same locations.

The value of the predicted UV index can be estimated from the map. The variation of the UV index is primarily influenced by the location on the globe and the time of year and day. Thick clouds can also absorb radiation effectively.

Due to cloudiness, differences in UV indexes can be observed even between nearby locations. However, the differences between locations at the same latitude in clear weather are usually smaller than the north-south differences.

Ozone depletion occurs in the latitudes of Finland in spring. Ozone depletion is an annual phenomenon and its duration and intensity vary from year to year depending on the meteorological conditions in the stratosphere.

In Finland, at the time of ozone depletion in spring the sun is still low, so the amount of UV radiation does not become dangerously strong. However, the UV radiation protection limit, i.e. UV index three, can be reached in those springs where ozone depletion still occurs in early April.

The ozone layer in the atmosphere protects life on Earth from the sun’s harmful ultraviolet radiation, i.e. UV radiation. The ozone layer also plays an important role in the radiation balance of the Earth’s atmosphere. In the early 1980s, scientists noticed that this natural sun protection was diminishing alarmingly above the South Pole region. In the springs, a so-called ozone hole formed above Antarctica. The reasons for the depletion of the ozone layer were soon found, and an international treaty, the Montreal Protocol, was signed in 1987, in which countries committed to stop using ozone-destroying compounds.

The World Meteorological Organization’s latest assessment report states that the ozone layer in the atmosphere will return to pre-1980s levels within the next four decades.