What is UV Radiation?

Ultraviolet (UV) radiation is invisible energy that comes from the sun. While it helps our bodies make Vitamin D, too much of it can be harmful, causing sunburn and other health risks. Understanding it is the first step to staying safe in the sun.

A diagram showing different types of sun rays reaching the earth

What are the Different Types of UV Light?

UV light is split into three types: UVA, UVB, and UVC.

UVA: Reaches the Earth and can cause skin aging and wrinkles.
UVB: Also reaches the Earth and is the main cause of sunburn. It also helps us make Vitamin D.
UVC: Is the strongest, but thankfully it is almost completely absorbed by the Earth's ozone layer.

Both UVA and UVB rays can harm your skin, so it's important to protect yourself from both.

What Do the UV Index Numbers Mean?

The UV Index measures the strength of UV rays on a scale from 0 to 11+. A higher number means you need more protection.

0-2 (Low): You can safely enjoy being outside.
3-5 (Moderate): Be careful. Seek shade during midday, wear a hat, and use sunscreen.
6-7 (High): Protection is a must. Reduce sun time between 10 a.m. and 4 p.m.
8-10 (Very High): Take extra care. Avoid being in the sun for too long.
11+ (Extreme): Be very cautious. Your skin can burn in just a few minutes.

How Can I Protect Myself from UV Rays?

When the UV index is 3 or higher, it's time to practice sun safety. Here are the five best ways to protect yourself:

Limit Midday Sun: The sun is strongest between 10 a.m. and 4 p.m.
Seek Shade: Use trees, umbrellas, or canopies to stay out of direct sunlight.
Wear Protective Clothing: A long-sleeved shirt and a wide-brimmed hat offer great protection.
Use Sunscreen: Use a broad-spectrum sunscreen with SPF 30 or higher. Reapply it every two hours.
Wear Sunglasses: Protect your eyes from UV damage with sunglasses that block UVA and UVB rays.

More Facts About UV Light

Green plants growing under sunlight

UV Light and Plants

Just like us, plants need sunlight. UV light helps them grow and develop, but too much can also cause damage to their leaves and cells.

Highest UV Index Ever Recorded

The highest UV index ever measured on Earth was a stunning 43.3 on a volcano in the Andes Mountains. For context, a normal "extreme" day on Earth is only 11!

Ready to check your city?

Now that you know all about UV radiation, find out what the UV index is in your location today! You can browse all cities or use the search.