If you travel to find the sun, you should also understand what it does to your skin. The UV index is the simplest tool for that: one number that tells you how quickly unprotected skin can burn. It is not the same as temperature, and that is exactly why it catches people out.
What the UV index measures
The UV index describes the strength of the sun's ultraviolet radiation at ground level, weighted by how strongly it causes sunburn. It is an international standard used by the World Health Organization (WHO) and weather services across Europe. The scale starts at 0 and has no fixed upper limit:
| UV index | Category | What it means |
|---|---|---|
| 0–2 | Low | Little risk for most people. |
| 3–5 | Moderate | Protection is recommended around midday. |
| 6–7 | High | Protection needed; seek shade at midday. |
| 8–10 | Very high | Extra protection; unprotected skin can burn quickly. |
| 11+ | Extreme | Avoid midday sun wherever possible. |
The WHO recommends sun protection whenever the index is 3 or higher.
Why UV has nothing to do with temperature
Ultraviolet radiation depends mainly on how high the sun is in the sky, not on how warm the air is. That leads to some surprises:
- Spring is sneaky. In late April and May the sun is already almost as high as in July and August, but the air is still cool. A fresh, clear May day in central or northern Europe can have a UV index of 5–6, while it feels like jacket weather. Many people get their first sunburn of the year this way.
- The south is stronger. Around midsummer, typical clear-sky UV peaks at about 5–6 in the Baltic states and Scandinavia, around 7–8 in central Europe and 8–10 or more on the Mediterranean.
- Winter sun is weaker, but not everywhere. In northern Europe the winter UV index stays around 0–1. In the Canary Islands it can reach moderate to high values even in December and January.
Midday matters most
UV is strongest when the sun is highest, around solar noon. In much of Europe during summer time, solar noon falls between about 13:00 and 14:00 local time, so the most intense period is roughly 11:00–16:00, not 12:00–14:00 as many people assume.
A simple rule from the WHO: if your shadow is shorter than you are, UV is high and you should protect yourself.
Clouds, altitude, snow and water
Clouds
Thin or scattered cloud blocks surprisingly little UV. According to the WHO, most UV radiation can pass through light cloud, and broken cloud can even increase UV briefly when sunlight is reflected from cloud edges. Only thick, dark overcast reduces it substantially. "It was cloudy, so I didn't bother" is one of the most common reasons for sunburn.
Altitude
UV increases with height, commonly cited as about 10% for every 1,000 m. On a sunny summer day in the Alps at 2,500 m, the UV index can be several points higher than in the valley below, even though it feels cooler.
Snow, sand and water
Surfaces reflect UV back at you:
- Fresh snow can reflect up to around 80%, which is why skiers burn under their chin and nose.
- Dry sand reflects around 15%.
- Sea foam reflects around 25%, and water itself lets UV through to a depth of about half a metre or more, so you can burn while swimming.
Combine altitude and snow on a clear spring day in the mountains, and the UV exposure can be extreme.
Practical protection
Sun protection is not about avoiding the sun, but about enjoying it longer:
- Plan around midday. On high-UV days, do your walking, cycling or sightseeing in the morning and late afternoon, and have a long lunch in the shade. The light is better for photos too.
- Clothing and a hat. A wide-brimmed hat and a shirt that covers the shoulders protect better than sunscreen alone.
- Sunglasses. Look for the CE mark with UV protection (UV400). Eyes can also be damaged by UV, especially near snow and water.
- Sunscreen. Use broad-spectrum protection of at least SPF 30. Apply generously 15–30 minutes before going out, and reapply every two hours and after swimming, towelling or sweating. Most people use far too little: an adult body needs around 30–35 ml for one application.
- Children. Children's skin burns more easily. Keep babies out of direct sun, and protect children with clothing, hats and shade first.
- Medication. Some medicines, such as certain antibiotics and acne treatments, increase sensitivity to light. Check the leaflet or ask a pharmacist before a sunny holiday.
Using the UV forecast on a trip
Most weather services publish a daily UV forecast, usually the expected maximum for clear skies. When you plan a sunny trip:
- Check the maximum UV as well as the temperature. A cool high in the mountains or in spring does not mean a low UV index.
- Adjust for altitude and surfaces if you are going into the mountains, onto the water or onto snow.
- Allow for your skin type. People with fair skin that burns easily need protection even at moderate values.
Chasing the sun is one of the pleasures of travel. Knowing the UV index lets you enjoy it all day without paying for it the day after.
This guide gives general information. If you have a skin condition, a history of skin cancer or questions about medication, ask a doctor or pharmacist.