We've all heard of the UV Index, but what is it and what does it measure?

We've all heard of the UV Index, but what is it and what does it measure?

The UV Index is a scale that measures the strength of the sun's ultraviolet (UV) radiation at the Earth's surface. The numbers, which start at zero, help people understand the risk of skin and eye damage from sun exposure.

UV radiation can cause sunburn, premature skin aging, eye damage such as cataracts, and an increased risk of skin cancer.

UV Index Categories

UV Index	Risk Level and Protection Recommended
0-2	Low Minimal protection needed
3-5	Moderate Wear sunscreen, sunglasses, and a hat
6-7	High Reduce time in the sun during midday hours
8-10	Very High Extra protection needed; seek shade
11+	Extreme Avoid prolonged sun exposure whenever possible

Why It Matters

The UV Index is useful for anyone planning outdoor activities. It helps you determine when sunscreen is needed, protects children and sensitive skin, and reduces the risk of long-term skin damage.

A common misconception is that a cool or cloudy day means the UV Index is low. UV rays can pass through clouds, and people can still get sunburned when temperatures are comfortable. Additionally, the sun can damage your skin in the winter months.

During summer, much of Canada typically sees UV Index values between 6 and 9 on sunny days, which falls into the High to Very High range. Even on cooler days, sun protection is often recommended during the middle of the day.

Choosing the right sunscreen

When choosing a sunscreen, several factors should be considered to ensure effective protection.

Check the SPF rating. Choose SPF 30 or higher for everyday use. SPF 30 blocks about 97% of UVB rays and SPF 50 blocks about 98% of UVB rays. Higher SPF provides slightly more protection, but no sunscreen blocks 100% of UV rays.

Choose a "broad-spectrum" product. This means the sunscreen protects against UVA rays, which contribute to skin aging and skin cancer, and UVB rays, which cause sunburn.

If you'll be swimming, sweating, or spending time at the beach, pick a sunscreen labelled water resistant (40 minutes) or water resistant (80 minutes). Reapply according to the label instructions, especially after swimming or heavy sweating.