Healthy Lifestyle

Understanding the UV Index – a Tool for When to Use Additional Sun Protection

Published: July 24, 2023

If you’re anything like me, knowing the weather conditions before stepping outside is essential.

Popular weather apps will tell you the current conditions, give you the projected high and low temperature for the day, and provide an hourly forecast. With a simple scroll, you’re able to find the 10-day outlook and other helpful measurements.

Among them is “UV index” – with a number between 1 and 11 displayed, along with “low,” “moderate,” “high,” “very high” or “extreme” listed under the number and sun protection recommendations.

But what does that number indicate? And what does it mean when it says, “Use sun protection until …”? How should you react to UV index information?


What Is the UV Index?

The UV index is a scale that forecasts how intense ultraviolet (UV) radiation is at a specific location and time of the day. It’s actually a complex equation based on cloud coverage, the amount of tree coverage, the altitude and latitude of your location, and what’s going on in the atmosphere.

The UV index isn’t measuring the temperature outside. It’s measuring something that’s invisible to us — the amount of UV exposure we might receive on that day in a specific location.

It’s possible to have a high UV index on a cool or cold day and a low UV index when it’s warmer. It’s not as straightforward as you might think, but it can serve as a reminder to make sure that you’re protected from the sun.


What Should I Do if the UV index Is High?

The higher the UV index number, the easier it is to get a sunburn. If you see the number is higher, you should consider using more sunscreen or even grabbing an umbrella to have an extra line of defense. And if you have plans that are flexible, you might consider changing them.

If the UV index is moderate or high, you should avoid being outside between 10 a.m. and 2 p.m. – when the sun’s rays are the strongest. Additionally, if you see instructions to use sun protection until a time after 2 p.m., consider adjusting your plans of being outside until after that time.

It’s possible that a high UV index might “feel” different depending on where you’re at when you’re looking at that number. Remember: The UV index is a measurement of the intensity of UV rays, not the temperature or humidity levels. That’s why a UV index of 8 in Omaha is different from an 8 in the Rocky Mountains or an 8 on either coast.

My hope is that you have a sun protection routine you follow every day. An understanding of the UV index should add to the precautions you’re already taking, but seeing a low UV index shouldn’t be an excuse to let your guard down.


General Sun Protection Guidelines

I urge everyone to have a daily routine — regardless of the UV index — that will have them well protected from the sun.

Regardless of the time of the year and what your plans are for the day, you should use a facial sunscreen with SPF of 30 or greater. This protection can be found in many face moisturizers and is a solid start to taking care of and protecting your skin year round.

Make sure that you apply broad spectrum sunscreen with a minimum SPF of 30 to any additional part of your body that could be exposed to the sun. And if you plan on spending extended time outside, make sure to use the following precautions.

  • Reapply sunscreen about every two hours or after swimming.
  • Wear a wide-brimmed hat, a sun-protected shirt — light weight and even long-sleeved, and sunglasses.
  • Avoid being outside when the UV index is high.

If you do get a sunburn, make sure to stay well-hydrated, use over-the-counter anti-inflammatory medicine like ibuprofen to help with the pain and apply moisturizers with aloe vera to soothe your skin.

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About the Author

Omaha native Tomas Huerta, MD, said it was always his dream to serve the community he grew up in. Dr. Huerta, a dermatologist with Methodist Physicians Clinic, is trained in Mohs micrographic surgery reconstructive facial plastic surgery. He believes in the importance of building relationships with his patients.

See more articles from Tomas Huerta, MD
Dr. Tomas Huerta