The UV Index, though widely reported, might not be on your mind when you’re checking the weather. It turns out, we all should probably pay it more mind. Though you can’t feel ultraviolet light the way you can feel temperature or humidity, the impact of a high UV day can have a huge impact.
UV radiation is a big risk factor for skin cancer, and staying safe isn’t just a matter of wearing SPF when it’s hot or really sunny.
We asked the experts to explain how we can best understand the UV Index, how to stay safe, and what we should know about extreme UV.
What is the UV Index?
Developed back in 1994, the UV Index is a measurement of how strong UV radiation is on a given day.
According to Davie, FL dermatologist Marianna Blyumin-Karasik, MD, there are several factors that determine that rating. “UV index is the gauge of ultraviolet radiation from the sun and can vary depending on region of the world, time of day, and season,” Dr. Blyumin-Karasik explains. “It is a spectrum from minimal level 0 to maximum level 11+. The more intense and harmful UV radiation, the higher is the measure of UV index, triggering UV Alert warning from the National Weather Service to be more careful about sun exposure at that time due to its harm, especially to the skin.”
According to West Palm Beach, FL dermatologist Kenneth Beer, MD, you can think of the index like a thermometer. “This is like a thermometer for light—the higher the number, the faster you will burn,” Dr. Beer explains.
What Should You Do to Stay Safe?
Because that number on the UV Index is based on so many factors, it isn’t as easy as just remembering to wear SPF when it’s sunny out. “You cannot feel UV radiation,” explains New York dermatologist Marina Peredo, MD. “So, a lot of people think they are safe on cloudy days because they don’t feel the direct sunlight. But that’s absolutely not true.”
Additionally, UV exposure is significantly greater at high altitudes compared to at sea level. Australia, for example, has consistently had the highest rates of skin cancer globally because of both its high altitude, sunny climate and susceptible population. But nearly every other member of the top 10 most high-risk countries for skin cancer were European countries, many of which were high above sea level.
“You could have a freezing cold day and get a lot of UV radiation,” Dr. Beer explains. “Think of Colorado.”
When we’re thinking about UV exposure, what’s considered safe is very minimal. “We really only consider the lower ends of the scale to be safe,” Dr. Beer says. “Typically, a 0 or 1.”
Most dermatologists will recommend wearing eye protection and SPF, even if the UV Index is projecting a low or moderate amount of exposure. This is because the amount of UV radiation you’re getting at a given time also depends on the time. UV radiation fluctuates and peaks around midday.
“If the rating is 8 or above, you really should not be outside, especially not at midday,” Dr. Peredo explains. “The sun is the strongest between 11 a.m. and 3 p.m. So, if you are outdoorsy, you should be trying to get in those experiences in the early morning or late afternoon.”
11+ Extreme on the UV Index
Any rating on the UV Index of 11 or higher is considered extreme and can cause a sunburn in as little as ten minutes. “In these cases, you should be limiting your exposure,” Dr. Beer says. “Wear UV protective clothing and physical sunblock, rather than chemical.”
Dr. Blyumin-Karasik agrees. “To protect yourself in situations of 11+ on the UV Index, you should stay indoors and seek shade,” she says. “You can also sun protect with sunscreen, sunglasses, and sun-protective clothing.”
It’s important to understand that while extreme heat and high UV often show up hand-in-hand, they aren’t always going to show up together.
New York dermatologist and spokesperson for The Skin Cancer Foundation, Ariel Ostad, MD explains that believing high UV and hot days are related is a common misconception. “The UV index can be just as high on a cool day as a hot one,” Dr. Ostad explains. “The UV is a measure of the intensity of the sun’s emitting energy. High heat does not always have a high UV index.”
Is UV Radiation Getting Worse?
There’s a layer of our atmosphere that acts as our planet’s sunscreen, and how well it’s doing can heavily impact how much UV radiation gets through to us and our fragile skin. This is the ozone layer, which sits in our stratosphere and shields from this kind of radiation.
You might remember having to leave behind your hairspray of choice back in the 80s, when a hole in the ozone layer of our atmosphere was discovered over Antarctica, sparking an international push to repair it.
According to NASA, there has been a lot of progress on repairing the ozone layer. But the work isn’t done yet.
“The ozone layer depletion due to the negative environmental impacts does enhance UV radiation,” Dr. Blyumin-Karasik explains.
The increase in UV radiation is most felt at mid-latitudes, where the amount of UV radiation has increased year-over-year in some areas as much as 20% since 1979. This may be one reason why it’s become more and more commonplace to experience a UV Index of 11 or higher.