Understanding the UV index: when sun protection is needed

What the UV index is

The UV index is an internationally uniform measure of the UV radiation that can cause sunburn. The higher the number, the faster unprotected skin can burn. The BfS compares the scale with the Richter scale for earthquakes: it is open at the top. It is also more than a measurement. It serves as a guide to which protective measures to take and when. For the definition, see the German glossary entry on the UV index. This guide is about how to read the number and what to do at which value. A German version is also available: UV-Index verstehen: Wann Schutz nötig ist.

The scale at a glance

The scale is divided into ranges with different recommendations. The table follows the BfS.

What to do at which value

At 1 to 2: usually no protection needed

According to the BfS table, no measures are normally required here. One caveat belongs to it: in summer, an index of 2 can last for several hours on cloudy days. During long stays outdoors, sunburn is then not ruled out, and the BfS advises using protective measures. The Krebsinformationsdienst, the cancer information service of the German Cancer Research Center, writes that sunburn is unlikely only below an index of 2. So 2 is more of a borderline than an all-clear. If you plan a long time outdoors, plan your protection too.

At 3 to 7: protection needed

From 3, the BfS recommends three things together:

• Seek shade during the midday hours.
• Wear suitable clothing, a hat and sunglasses.
• Use a sun protection product with an adequate sun protection factor on uncovered skin.

How much cream your face needs and how often to reapply is calculated by the German-language sun protection tool for the face. What to look for on the label when you buy is covered in Sonnenschutz kaufen: Kriterien fürs Gesicht, a German-language page marked as unpaid and without commission.

At 8 and higher: protection absolutely necessary

From 8, the BfS recommendations become stricter. Avoid being outdoors at midday if you can, shade is a must, and clothing, hat, sunglasses and sun cream with an adequate sun protection factor are urgently needed. In Germany, values of 8 to 9 are reached in summer, and up to 11 in the high-altitude regions of southern Germany. Near the equator, values of 12 and higher can occur.

Why the value changes: time, season, place

The UV index depends mainly on the position of the sun. It therefore changes most with the season, the time of day and the latitude. The ozone concentration in the atmosphere, cloud cover and altitude also play a part.

• Time of day: The BfS shows the measured sunburn-relevant radiation as a curve that rises and falls over the day. A forecast figure, by contrast, is a single value for the day, so look at the highest value rather than at the one for your current hour.
• Season: The index is highest in summer. The Krebsinformationsdienst points out that an index of 2 can be exceeded in Germany under a cloudless sky as early as the end of March. Spring is therefore not a period without a need for protection.
• Place: The value is the same worldwide. It was defined by the WHO, and according to the BfS an index of 7 in Germany means exactly the same as in Kenya or Canada. Altitude matters too: the higher you are, the stronger the UV radiation, which is why more protection is needed in the mountains.

Where the index can mislead you

Clouds. Light cloud cover hardly lowers the UV index. In special cloud situations it can even rise briefly above the value for a clear sky because of scattered radiation. The Krebsinformationsdienst adds that a thin layer of cloud holds back hardly any UV radiation. According to the BfS, people cannot see or feel UV radiation with any sense. How warm it feels therefore says nothing about the UV exposure.

Reflection. Snow, water and light surfaces such as bright house façades, asphalt or sand reflect UV radiation and strengthen it. The exposure can then be higher than the stated index. In such situations adequate sun protection is particularly important, says the BfS.

Shade. The Krebsinformationsdienst states that shade alone is not sufficient UV protection. It quotes figures from the Federal Institute for Occupational Safety and Health: a tree corresponds roughly to a sun cream with a sun protection factor between 5 and 15, a parasol, depending on size and fabric, to a factor between 5 and 40. Shade helps, but it is not complete protection.

Where to find the current value

Current values and forecasts are published by the BfS, with the German Weather Service (DWD) as a supplement.

If you are unsure

A simple rule for everyday life: look at the highest value of the day. If it is 3 or above, plan for protection, even with clouds and even in spring. At 8 and higher, move time outdoors away from midday where you can. Clothing, a hat and sunglasses are part of the protection just as much as the cream.

Tip from Luljeta Dine

Take a short look at the day's UV index in the morning, before you get dressed. It takes ten seconds and tells you how much protection to plan for.

When to see a doctor

This guide explains protection from UV radiation, not skin diseases, and it makes no diagnosis. According to the BfS, UV radiation causes sunburn, premature skin ageing and skin cancer. If you are unsure whether you need special UV protection, for example because of earlier skin cancer, skin cancer in the family or certain pigment spots, you can ask a doctor; the Krebsinformationsdienst names dermatologists as suitable contacts. If you go beyond your skin's own protection time, according to the BfS (quoted by the Krebsinformationsdienst), pain, burns with blisters and possibly fever are possible. With such symptoms, and with any skin change that worries you, a doctor should assess it. Artificial UV radiation, as in a sunbed, is clearly carcinogenic according to the Krebsinformationsdienst, which strongly advises against sunbeds.

Read on

• Skincare and cosmetics: guide: the overview of facial skincare
• UV-Index verstehen: Wann Schutz nötig ist: the German version of this guide
• Sonnenschutz fürs Gesicht: calculate amount, sun protection factor and reapplying (German)
• UV-Index: the definition in the German glossary
• Sonnenschutz kaufen: Kriterien fürs Gesicht: selection criteria on the label, unpaid and without commission (German)