UV Index Explained: Levels & How to Protect Yourself

The UV index tells you how strong the sun’s ultraviolet (UV) rays are on a given day. UV rays cause sunburn, skin aging and skin cancer, and you cannot feel them: a cool or cloudy day can still have a high UV index. Here is what the numbers mean and how to protect yourself.

UV Index Explained: What the Numbers Mean and How to Protect Your Skin

Quick answer

UV index 3 or higher: protect your skin and eyes.
Seek shade around midday (roughly 10 am to 4 pm), when UV is strongest.
Use broad-spectrum sunscreen SPF 30 or higher, apply generously and reapply every 2 hours.
Wear a hat, sunglasses and clothing that covers your skin.

The UV index scale

UV index	Level	What to do
0–2	Low	Little protection needed for most people. Wear sunglasses on bright days.
3–5	Moderate	Seek shade at midday, cover up, wear a hat, sunglasses and sunscreen.
6–7	High	Reduce time in the sun between 10 am and 4 pm. Full protection.
8–10	Very high	Extra protection. Unprotected skin can burn quickly. Avoid the midday sun.
11+	Extreme	Avoid being outside at midday. Unprotected skin can burn in minutes.

You can find the daily UV index in most weather apps and forecasts.

Why UV rays are harmful

UVB rays cause sunburn and play a major role in skin cancer.
UVA rays penetrate deeper, cause skin aging and wrinkles, and also contribute to skin cancer. They pass through clouds and window glass.
UV also damages the eyes and can contribute to cataracts.

What makes UV stronger?

Time of day: highest around midday.
Season and location: stronger in summer and closer to the equator.
Altitude: UV increases the higher you go, which matters in the mountains.
Reflection: snow reflects up to 80% of UV; sand, water and concrete also reflect it.
Clouds: thin clouds let most UV through, so you can still burn on an overcast day.

Shadow rule: if your shadow is shorter than you are, UV is strong. Seek shade.

How to protect yourself

1. Seek shade

Especially in the middle of the day. Remember that shade reduces but does not block all UV, because rays reflect off surfaces.

2. Cover up

Wear long sleeves and trousers or skirts in tightly woven fabric, a wide-brimmed hat that shades the face, ears and neck, and sunglasses that block 100% of UVA and UVB.

3. Use sunscreen correctly

Choose broad-spectrum (UVA and UVB) sunscreen with SPF 30 or higher.
Apply generously, about a shot glass (30 ml) for an adult’s body, 15 minutes before going out.
Reapply every 2 hours and after swimming, sweating or towel-drying.
Do not forget ears, neck, the tops of feet and the scalp if your hair is thin.
Sunscreen is one layer of protection, not a reason to stay in strong sun longer.

4. Protect children

Children’s skin burns easily. Keep babies under 6 months out of direct sun, and use shade, clothing, hats and sunscreen for older children.

5. Skip sunbeds

Tanning beds give off strong UV and increase the risk of skin cancer, including melanoma.

What about vitamin D?

Your skin makes vitamin D from sunlight, but you do not need to burn or tan to get it. Short periods of everyday sun exposure are usually enough in summer. In winter, or if you cover most of your skin, ask your doctor about a vitamin D supplement.